How do I check if an array includes a value in JavaScript

Question

What is the most concise and efficient way to find out if a JavaScript array contains a value  This is the only way I know to do it  function contains a  obj        for  var i   0  i  lt  a length  i              if  a i      obj                return true                      return false     Is there a better and more concise way to accomplish this

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Extending the JavaScript Array object is a really bad idea because you introduce new properties  your custom methods  into for-in loops which can break existing scripts  A few years ago the authors of the Prototype library had to re-engineer their library implementation to remove just this kind of thing   If you don t need to worry about compatibility with other JavaScript running on your page  go for it  otherwise  I d recommend the more awkward  but safer free-standing function solution

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Update from 2019  This answer is from 2008  11 years old   and is not relevant for modern JS usage  The promised performance improvement was based on a benchmark done in browsers of that time  It might not be relevant to modern JS execution contexts  If you need an easy solution  look for other answers  If you need the best performance  benchmark for yourself in the relevant execution environments   As others have said  the iteration through the array is probably the best way  but it has been proven that a decreasing while loop is the fastest way to iterate in JavaScript  So you may want to rewrite your code as follows   function contains a  obj        var i   a length      while  i--           if  a i      obj               return true                     return false      Of course  you may as well extend Array prototype   Array prototype contains   function obj        var i   this length      while  i--            if  this i      obj                return true                      return false      And now you can simply use the following   alert  1  2  3  contains 2         gt  true alert  1  2  3  contains  2          gt  false

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By no means the best  but I was just getting creative and adding to the repertoire  Do not use this  x000D   x000D  Object defineProperty Array prototype   exists       value  function element  index         var index   index    0      return index     this length   -1   this index      element   index   this exists element    index              Outputs 1 console log   one    two   exists  two         Outputs -1 console log   one    two   exists  three      console log   one    two    three    four   exists  four     x000D   x000D   x000D

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OK  you can just optimise your code to get the result    There are many ways to do this which are cleaner and better  but I just wanted to get your pattern and apply to that using JSON stringify  just simply do something like this in your case   function contains a  obj        for  var i   0  i  lt  a length  i              if  JSON stringify a i       JSON stringify obj                 return true                      return false

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Use   var myArray     yellow    orange    red      alert    myArray indexOf  red       true   Demo  To know exactly what the tilde   do at this point  refer to this question What does a tilde do when it precedes an expression

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function contains a  obj        return a some function element  return element    obj        Array prototype some   was added to the ECMA-262 standard in the 5th edition

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Literally   using Firefox v3 6  with for-in caveats as previously noted  HOWEVER the use below might endorse for-in for this very purpose  That is  enumerating array elements that ACTUALLY exist via a property index  HOWEVER  in particular  the array length property is NOT enumerated in the for-in property list        Drag  amp  drop the following complete URI s for immediate mode browser testing   JavaScript    function ObjInRA ra  var has false  for i in ra  has true  break   return has      function check ra         return   There is   ObjInRA ra   an   NO    object in    ra       join           alert               check        check      check   2 3                check          t  a null string    check                  join   n      which displays  There is an object in   object Object    There is NO object in     There is an object in   2 3   There is an object in           a null string  There is NO object in        Wrinkles  if looking for a  quot specific quot  object consider  JavaScript  alert          alert           And thus  JavaScript   obj    prop  quot value quot      ra1    obj     ra2     prop  quot value quot      alert ra1 0     obj     alert ra2 0     obj    Often ra2 is considered to  quot contain quot  obj as the literal entity  prop  quot value quot    A very coarse  rudimentary  naive  as in code needs qualification enhancing  solution  JavaScript    obj  prop  quot value quot      ra2   prop  quot value quot       alert      ra2   toSource     indexOf  obj toSource   match             1       -1          found           missing      See ref  Searching for objects in JavaScript arrays

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Use includes javascript in-build function  but not work in Internet Explorer  var optval        optval push  A        optval push  B        optval push  C      We can search string A in javascript array as   optval includes  A            gt  return true

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Thinking out of the box for a second  if you are making this call many many times  it is vastly more efficient to use an associative array a Map to do lookups using a hash function   https   developer mozilla org en-US docs Web JavaScript Reference Global Objects Map

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Just another option     usage  if     a   b   c   d   contains  b             Array prototype contains   function value       for  var key in this          if  this key      value  return true      return false      Be careful because overloading javascript array objects with custom methods can disrupt the behavior of other javascripts  causing unexpected behavior

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Use includes javascript in-build function  but not work in Internet Explorer  var optval        optval push  A        optval push  B        optval push  C      We can search string A in javascript array as   optval includes  A            gt  return true

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I recommended to use underscore library because its return the value and its supported for all browsers    underscorejs   var findValue     find array  function item        return item id    obj id

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Adding a unique item to a another list  searchResults                                          name   Hello                       artist   Selana                       album   Riga                       id  1                                                           name   Hello s                       artist   Selana G                       album   Riga1                       id  2                                                           name   Hello2                       artist   Selana                       album   Riga11                       id  3                                               playlistTracks                                    name   Hello                   artist   Mamunuus                   album   Riga                   id  4                                                   name   Hello s                   artist   Mamunuus G                   album   Riga1                   id  2                                                   name   Hello2                   artist   Mamunuus New                   album   Riga11                   id  3                                             playlistName   New PlayListTrack                            Adding an unique track in the playList     addTrack   track   gt          if playlistTracks find savedTrack   gt  savedTrack id     track id             return                playlistTracks push track          this setState           playlistTracks

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While array indexOf x   -1 is the most concise way to do this  and has been supported by non-Internet nbsp Explorer browsers for over decade      it is not O 1   but rather O N   which is terrible  If your array will not be changing  you can convert your array to a hashtable  then do table x    undefined or    undefined   Array prototype toTable   function         var t           this forEach function x  t x  true        return t      Demo   var toRemove    2 4  toTable     1 2 3 4 5  filter function x  return toRemove x    undefined      Unfortunately  while you can create an Array prototype contains to  freeze  an array and store a hashtable in this  cache in two lines  this would give wrong results if you chose to edit your array later  JavaScript has insufficient hooks to let you keep this state  unlike Python for example

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Performance  Today 2020 01 07 I perform tests on MacOs HighSierra 10 13 6 on Chrome v78 0 0  Safari v13 0 4 and Firefox v71 0 0 for 15 chosen solutions  Conclusions   solutions based on JSON  Set and surprisingly find  K N O  are slowest on all browsers the es6 includes  F  is fast only on chrome the solutions based on for  C D  and indexOf  G H  are quite-fast on all browsers on small and big arrays so probably they are best choice for efficient solution the solutions where index decrease during loop   B  is slower probably because the way of CPU cache works   I also run test for big array when searched element was on position 66  of array length  and solutions based on for  C D E  gives similar results   630 ops sec - but the E on safari and firefox was 10-20  slower than C and D    Results    Details  I perform 2 tests cases  for array with 10 elements  and array with 1 milion elements  In both cases we put searched element in the array middle    x000D   x000D  let log    name f    gt  console log    name   3-  f arr  s10      s7 -  f arr  s7     6-  f arr 6    s3 -  f arr  s3      x000D   x000D  let arr    1 2 3 4 5  s6   s7   s8   s9   s10    x000D    arr   new Array 1000000  fill 123   arr 500000  7  x000D   x000D  function A a  val    x000D      var i   -1  x000D      var n   a length  x000D      while  i   lt n    x000D         if  a i      val    x000D             return true  x000D           x000D        x000D      return false  x000D    x000D   x000D  function B a  val    x000D      var i   a length  x000D      while  i--    x000D         if  a i      val    x000D             return true  x000D           x000D        x000D      return false  x000D    x000D   x000D  function C a  val    x000D      for  var i   0  i  lt  a length  i      x000D          if  a i      val  return true  x000D        x000D      return false  x000D    x000D   x000D  function D a val  x000D    x000D      var len   a length  x000D      for var i   0   i  lt  len i    x000D        x000D          if a i      val  return true  x000D        x000D      return false  x000D     x000D   x000D  function E a  val     x000D    var n   a length-1  x000D    var t   n 2  x000D    for  var i   0  i  lt   t  i      x000D          if  a i      val    a n-i      val  return true  x000D      x000D    return false  x000D    x000D   x000D  function F a val    x000D   return a includes val   x000D    x000D   x000D  function G a val    x000D   return a indexOf val  gt  0  x000D    x000D   x000D  function H a val    x000D   return    a indexOf val   x000D    x000D   x000D  function I a  val    x000D    return a findIndex x  gt  x  val  gt  0  x000D    x000D   x000D  function J a val    x000D   return a some x  gt  x   val   x000D    x000D   x000D  function K a  val    x000D    const s   JSON stringify val   x000D    return a some x   gt  JSON stringify x      s   x000D    x000D   x000D  function L a val    x000D   return  a every x  gt  x   val   x000D    x000D   x000D  function M a  val    x000D    return   a find x  gt  x  val   x000D    x000D   x000D  function N a val    x000D   return a filter x  gt x   val  length  gt  0  x000D    x000D   x000D  function O a  val    x000D    return new Set a  has val   x000D    x000D   x000D  log  A  A   x000D  log  B  B   x000D  log  C  C   x000D  log  D  D   x000D  log  E  E   x000D  log  F  F   x000D  log  G  G   x000D  log  H  H   x000D  log  I  I   x000D  log  J  J   x000D  log  K  K   x000D  log  L  L   x000D  log  M  M   x000D  log  N  N   x000D  log  O  O   x000D  This shippet only presents functions used in performance tests - it not perform tests itself  x000D   x000D   x000D    Array small - 10 elements  You can perform tests in your machine HERE    Array big - 1 000 000 elements  You can perform tests in your machine HERE

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Using idnexOf   it is a good solution  but you should hide embedded implementation indexOf   function which returns -1 with   operator    function include arr obj         return     arr indexOf obj

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Simple solution   ES6 Features   includes  method   let arr    1  2  3  2  3  2  3  4      arr includes 2     true    arr includes 93     false

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function contains a  obj        return a some function element  return element    obj        Array prototype some   was added to the ECMA-262 standard in the 5th edition

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You can use findIndex function to check if an array has a specific value  arrObj findIndex obj   gt  obj     comparedValue      -1   Returns true if arrObj contains comparedValue  false otherwise

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One-liner   function contains arr  x        return arr filter function elem    return elem    x    length  gt  0

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It has one parameter  an array numbers of objects  Each object in the array has two integer properties denoted by x and y  The function must return a count of all such objects in the array that satisfy numbers x    numbers y   x000D   x000D  var numbers       x  1  y  1    x000D                    x  2  y  3    x000D                    x  3  y  3    x000D                    x  3  y  4    x000D                    x  4  y  5      x000D  var count   0   x000D  var n   numbers length  x000D  for  var i  0 i lt n i    x000D    x000D    if numbers i  x  numbers i  y  x000D       count  1   x000D    x000D   x000D  alert count   x000D   x000D   x000D

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indexOf maybe  but it s a  JavaScript extension to the ECMA-262 standard  as such it may not be present in other implementations of the standard    Example    1  2  3  indexOf 1    gt  0   foo    bar    baz   indexOf  bar     gt  1  1  2  3  indexOf 4    gt  -1   AFAICS Microsoft does not offer some kind of alternative to this  but you can add similar functionality to arrays in Internet Explorer  and other browsers that don t support indexOf  if you want to  as a quick Google search reveals  for example  this one

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I recommended to use underscore library because its return the value and its supported for all browsers    underscorejs   var findValue     find array  function item        return item id    obj id

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Solution that works in all modern browsers   function contains arr  obj      const stringifiedObj   JSON stringify obj      Cache our object to not call  JSON stringify  on every iteration   return arr some item   gt  JSON stringify item      stringifiedObj       Usage   contains   a  1    a  2     a  1       true   IE6  solution   function contains arr  obj      var stringifiedObj   JSON stringify obj    return arr some function  item        return JSON stringify item      stringifiedObj               some polyfill  not needed for IE9  if     some  in Array prototype       Array prototype some   function  tester  that   opt          for  var i   0  n   this length  i  lt  n  i            if  i in this  amp  amp  tester call that  this i   i  this   return true        return false           Usage   contains   a  1    a  2     a  1       true   Why to use JSON stringify   Array indexOf and Array includes  as well as most of the answers here  only compare by reference and not by value     a  1    a  2   includes  a  1       false  because  a  1  is a new object   Bonus  Non-optimized ES6 one-liner     a  1    a  2   some item   gt  JSON stringify item      JSON stringify  a  1       true     Note  Comparing objects by value will work better if the keys are in the same order  so to be safe you might sort the keys first with a package like this one  https   www npmjs com package sort-keys    Updated the contains function with a perf optimization  Thanks itinance for pointing it out

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Use lodash s some function   It s concise  accurate and has great cross platform support   The accepted answer does not even meet the requirements   Requirements  Recommend most concise and efficient way to find out if a JavaScript array contains an object   Accepted Answer     inArray   b   2      a   1     b   2     gt  -1   My recommendation     some    a   1     b   2      b   2    gt  true   Notes      inArray works fine for determining whether a scalar value exists in an array of scalars       inArray 2   1 2    gt  1       but the question clearly asks for an efficient way to determine if an object is contained in an array   In order to handle both scalars and objects  you could do this      isObject item       some ary  item       indexOf ary  item   gt  -1

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Or this solution   Array prototype includes   function  object      return     this indexOf object

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indexOf maybe  but it s a  JavaScript extension to the ECMA-262 standard  as such it may not be present in other implementations of the standard    Example    1  2  3  indexOf 1    gt  0   foo    bar    baz   indexOf  bar     gt  1  1  2  3  indexOf 4    gt  -1   AFAICS Microsoft does not offer some kind of alternative to this  but you can add similar functionality to arrays in Internet Explorer  and other browsers that don t support indexOf  if you want to  as a quick Google search reveals  for example  this one

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Update from 2019  This answer is from 2008  11 years old   and is not relevant for modern JS usage  The promised performance improvement was based on a benchmark done in browsers of that time  It might not be relevant to modern JS execution contexts  If you need an easy solution  look for other answers  If you need the best performance  benchmark for yourself in the relevant execution environments   As others have said  the iteration through the array is probably the best way  but it has been proven that a decreasing while loop is the fastest way to iterate in JavaScript  So you may want to rewrite your code as follows   function contains a  obj        var i   a length      while  i--           if  a i      obj               return true                     return false      Of course  you may as well extend Array prototype   Array prototype contains   function obj        var i   this length      while  i--            if  this i      obj                return true                      return false      And now you can simply use the following   alert  1  2  3  contains 2         gt  true alert  1  2  3  contains  2          gt  false

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Surprised that this question still doesn t have latest syntax added  adding my 2 cents   Let s say we have array of Objects arrObj and we want to search obj in it   Array prototype indexOf -   returns index or -1  is generally used for finding index of element in array  This can also be used for searching object but only works if you are passing reference to same object   let obj     name   Sumer   age  36    let arrObj    obj    name   Kishor   age  46      name   Rupen   age  26       console log arrObj indexOf obj      0 console log arrObj indexOf   name   Sumer   age  36        -1  console log  1  3  5  2  indexOf 2      3   Array prototype includes -   returns true or false   console log arrObj includes obj       true console log arrObj includes   name   Sumer   age  36        false  console log  1  3  5  2  includes 2      true   Array prototype find -   takes callback  returns first value object that returns true in CB    console log arrObj find e   gt  e age  gt  40         name   Kishor   age  46   console log arrObj find e   gt  e age  gt  40        name   Kishor   age  46    console log  1  3  5  2  find e   gt  e  gt  2      3   Array prototype findIndex -   takes callback  returns index of first value object that returns true in CB    console log arrObj findIndex e   gt  e age  gt  40       1 console log arrObj findIndex e   gt  e age  gt  40      1  console log  1  3  5  2  findIndex e   gt  e  gt  2      1   Since find and findIndex takes a callback  we can be fetch any object even if we don t have the reference  from array by creatively setting the true condition

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Here s how Prototype does it           Array indexOf item   offset   0   - gt  Number     - item      A value that may or may not be in the array      - offset  Number   The number of initial items to skip before beginning the         search         Returns the position of the first occurrence of  item  within the array  amp mdash  or      -1  if  item  doesn t exist in the array      function indexOf item  i      i     i   0     var length   this length    if  i  lt  0  i   length   i    for    i  lt  length  i        if  this i      item  return i    return -1      Also see here for how they hook it up

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ECMAScript 7 introduces Array prototype includes   It can be used like this    1  2  3  includes 2      true  1  2  3  includes 4      false   It also accepts an optional second argument fromIndex    1  2  3  includes 3  3      false  1  2  3  includes 3  -1      true   Unlike indexOf  which uses Strict Equality Comparison  includes compares using SameValueZero equality algorithm  That means that you can detect if an array includes a NaN    1  2  NaN  includes NaN      true   Also unlike indexOf  includes does not skip missing indices   new Array 5  includes undefined      true   Currently it s still a draft but can be polyfilled to make it work on all browsers

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In Addition to what others said  if you don t have a reference of the object which you want to search in the array  then you can do something like this   let array    1  2  3  4    key    value      array some  element    gt  JSON stringify element      JSON stringify   key    value        true  array some  element    gt  JSON stringify element      JSON stringify         true   Array some returns true if any element matches the given condition and returns false if none of the elements matches the given condition

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We use this snippet  works with objects  arrays  strings           function     name Object prototype inArray     description Extend Object prototype within inArray function        param  mix     needle       - Search-able needle     param  bool    searchInKey  - Search needle in keys         Object defineProperty Object prototype   inArray        value  function needle  searchInKey            var object   this           if  Object prototype toString call needle        object Object                   Object prototype toString call needle        object Array                 needle   JSON stringify needle                      return Object keys object  some function key                var value   object key                if  Object prototype toString call value        object Object                       Object prototype toString call value        object Array                     value   JSON stringify value                              if searchInKey                   if value     needle    key     needle                   return true                                 else                  if value     needle                       return true                                                         writable  true      configurable  true      enumerable  false       Usage   var a    one   first   two   second   foo   three   third     a inArray  first               true a inArray  foo                 false a inArray  foo   true          true - search by keys a inArray  three   third       true  var b     one    two    three    four    foo   val     b inArray  one              true b inArray  foo              false b inArray  foo   val        true b inArray   foo   val       false  var c    String   c inArray  S             true c inArray  s             false c inArray  2   true      true c inArray  20   true     false

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Literally   using Firefox v3 6  with for-in caveats as previously noted  HOWEVER the use below might endorse for-in for this very purpose  That is  enumerating array elements that ACTUALLY exist via a property index  HOWEVER  in particular  the array length property is NOT enumerated in the for-in property list        Drag  amp  drop the following complete URI s for immediate mode browser testing   JavaScript    function ObjInRA ra  var has false  for i in ra  has true  break   return has      function check ra         return   There is   ObjInRA ra   an   NO    object in    ra       join           alert               check        check      check   2 3                check          t  a null string    check                  join   n      which displays  There is an object in   object Object    There is NO object in     There is an object in   2 3   There is an object in           a null string  There is NO object in        Wrinkles  if looking for a  quot specific quot  object consider  JavaScript  alert          alert           And thus  JavaScript   obj    prop  quot value quot      ra1    obj     ra2     prop  quot value quot      alert ra1 0     obj     alert ra2 0     obj    Often ra2 is considered to  quot contain quot  obj as the literal entity  prop  quot value quot    A very coarse  rudimentary  naive  as in code needs qualification enhancing  solution  JavaScript    obj  prop  quot value quot      ra2   prop  quot value quot       alert      ra2   toSource     indexOf  obj toSource   match             1       -1          found           missing      See ref  Searching for objects in JavaScript arrays

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Here s a JavaScript 1 6 compatible implementation of Array indexOf   if   Array indexOf        Array indexOf      indexOf           function arr  obj  from                return arr indexOf obj  from                       function arr  obj  from        for IE6              var l   arr length                  i   from   parseInt  1   from     from  lt  0   l   0   10    0              i   i  lt  0   0   i              for    i  lt  l  i                      if  i in arr  amp  amp  arr i      obj                        return i                                              return -1

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Use   var myArray     yellow    orange    red      alert    myArray indexOf  red       true   Demo  To know exactly what the tilde   do at this point  refer to this question What does a tilde do when it precedes an expression

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I was working on a project that I needed a functionality like python set which removes all duplicates values and returns a new list  so I wrote this function maybe useful to someone  function set arr        var res           for  var i   0  i  lt  arr length  i              if  res indexOf arr i       -1                res push arr i                        return res

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Use   Array prototype contains   function x     var retVal   -1        x is a primitive type   if   string   number   indexOf typeof x  gt  0    retVal   this indexOf x          x is a function   else if typeof x    function   for var ix in this       if  this ix        x      retVal   ix           x is an object      else       var sx JSON stringify x       for var ix in this         if typeof this ix     object   amp  amp  JSON stringify this ix    sx  retVal   ix                 Return False if -1 else number if numeric otherwise string   return  retVal     -1  false     isNaN  retVal    retVal    retVal       I know it s not the best way to go  but since there is no native IComparable way to interact between objects  I guess this is as close as you can get to compare two entities in an array  Also  extending Array object might not be a wise thing to do  but sometimes it s OK  if you are aware of it and the trade-off

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Let s say you ve defined an array like so   const array    1  2  3  4    Below are three ways of checking whether there is a 3 in there  All of them return either true or false   Native Array method  since ES2016   compatibility table   array includes 3     true   As custom Array method  pre ES2016      Prefixing the method with     to avoid name clashes Object defineProperty Array prototype    includes     value  function  v    return this indexOf v      -1     array  includes 3     true   Simple function  const includes    a  v    gt  a indexOf v      -1 includes array  3     true

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The top answers assume primitive types but if you want to find out if an array contains an object with some trait  Array prototype some   is an elegant solution  const items      a   1     a   2     a   3      items some item   gt  item a      3       returns true items some item   gt  item a      4       returns false  The nice thing about it is that the iteration is aborted once the element is found so unnecessary iteration cycles are spared  Also  it fits nicely in an if statement since it returns a boolean  if  items some item   gt  item a      3           do something      As jamess pointed out in the comment  at the time of this answer  September 2018  Array prototype some   is fully supported  caniuse com support table

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You can use findIndex function to check if an array has a specific value  arrObj findIndex obj   gt  obj     comparedValue      -1   Returns true if arrObj contains comparedValue  false otherwise

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The top answers assume primitive types but if you want to find out if an array contains an object with some trait  Array prototype some   is an elegant solution  const items      a   1     a   2     a   3      items some item   gt  item a      3       returns true items some item   gt  item a      4       returns false  The nice thing about it is that the iteration is aborted once the element is found so unnecessary iteration cycles are spared  Also  it fits nicely in an if statement since it returns a boolean  if  items some item   gt  item a      3           do something      As jamess pointed out in the comment  at the time of this answer  September 2018  Array prototype some   is fully supported  caniuse com support table

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ECMAScript 6 has an elegant proposal on find      The find method executes the callback function once for each element   present in the array until it finds one where callback returns a true   value  If such an element is found  find immediately returns the value   of that element  Otherwise  find returns undefined  callback is   invoked only for indexes of the array which have assigned values  it   is not invoked for indexes which have been deleted or which have never   been assigned values    Here is the MDN documentation on that   The find functionality works like this   function isPrime element  index  array        var start   2      while  start  lt   Math sqrt element             if  element   start    lt  1  return false            return  element  gt  1      console log   4  6  8  12  find isPrime        Undefined  not found console log   4  5  8  12  find isPrime        5   You can use this in ECMAScript 5 and below by defining the function   if   Array prototype find      Object defineProperty Array prototype   find         enumerable  false      configurable  true      writable  true      value  function predicate          if  this    null            throw new TypeError  Array prototype find called on null or undefined                  if  typeof predicate      function             throw new TypeError  predicate must be a function                  var list   Object this         var length   list length  gt  gt  gt  0        var thisArg   arguments 1         var value         for  var i   0  i  lt  length  i              if  i in list              value   list i             if  predicate call thisArg  value  i  list                 return value                                      return undefined

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Here s how Prototype does it           Array indexOf item   offset   0   - gt  Number     - item      A value that may or may not be in the array      - offset  Number   The number of initial items to skip before beginning the         search         Returns the position of the first occurrence of  item  within the array  amp mdash  or      -1  if  item  doesn t exist in the array      function indexOf item  i      i     i   0     var length   this length    if  i  lt  0  i   length   i    for    i  lt  length  i        if  this i      item  return i    return -1      Also see here for how they hook it up

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You can also use this trick   var arrayContains   function object      return  serverList filter function currentObject        if  currentObject     object          return currentObject           else         return false             length  gt  0    true   false

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Use   Array prototype contains   function x     var retVal   -1        x is a primitive type   if   string   number   indexOf typeof x  gt  0    retVal   this indexOf x          x is a function   else if typeof x    function   for var ix in this       if  this ix        x      retVal   ix           x is an object      else       var sx JSON stringify x       for var ix in this         if typeof this ix     object   amp  amp  JSON stringify this ix    sx  retVal   ix                 Return False if -1 else number if numeric otherwise string   return  retVal     -1  false     isNaN  retVal    retVal    retVal       I know it s not the best way to go  but since there is no native IComparable way to interact between objects  I guess this is as close as you can get to compare two entities in an array  Also  extending Array object might not be a wise thing to do  but sometimes it s OK  if you are aware of it and the trade-off

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This may be a detailed and easy solution     plain array var arr     a    b    c    var check   arr includes  a    console log check     returns true if  check          value exists in array      write some codes       array with objects var arr            x  a   y  b           x  p   y  q            if you want to check if x  p  exists in arr var check   arr filter function  elm       if  elm x     p                return elm     returns length   1  object exists in array                or y  q  exists in arr var check   arr filter function  elm       if  elm y     q                return elm     returns length   1  object exists in array                if you want to check  if the entire object  x  p   y  q   exists in arr var check   arr filter function  elm       if  elm x     p   amp  amp  elm y     q                return elm     returns length   1  object exists in array                in all cases console log check length      returns 1  if  check length  gt  0          returns true       object exists in array      write some codes

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use Array prototype includes for example   x000D   x000D  const fruits     coconut    banana    apple    const doesFruitsHaveCoconut   fruits includes  coconut     true  console log doesFruitsHaveCoconut  x000D   x000D   x000D   maybe read this documentation from MDN  https   developer mozilla org en-US docs Web JavaScript Reference Global Objects Array includes

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Here s a JavaScript 1 6 compatible implementation of Array indexOf   if   Array indexOf        Array indexOf      indexOf           function arr  obj  from                return arr indexOf obj  from                       function arr  obj  from        for IE6              var l   arr length                  i   from   parseInt  1   from     from  lt  0   l   0   10    0              i   i  lt  0   0   i              for    i  lt  l  i                      if  i in arr  amp  amp  arr i      obj                        return i                                              return -1

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Thinking out of the box for a second  if you are making this call many many times  it is vastly more efficient to use an associative array a Map to do lookups using a hash function   https   developer mozilla org en-US docs Web JavaScript Reference Global Objects Map

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Object keys for getting all property names of the object and filter all values that exact or partial match with specified string   x000D   x000D  function filterByValue array  string      return array filter o   gt      Object keys o  some k   gt  o k  toLowerCase   includes string toLowerCase          const arrayOfObject        name   Paul     country   Canada          name   Lea     country   Italy          name   John     country   Italy       console log filterByValue arrayOfObject   lea          name   Lea   country   Italy    console log filterByValue arrayOfObject   ita          name   Lea   country   Italy     name   John   country   Italy    x000D   x000D   x000D   You can also filter by specific key such as  Object keys o  some k   gt  o country toLowerCase   includes string toLowerCase        Now you can just check array count after filtered to check value contains or not  Hope it s helpful

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Update from 2019  This answer is from 2008  11 years old   and is not relevant for modern JS usage  The promised performance improvement was based on a benchmark done in browsers of that time  It might not be relevant to modern JS execution contexts  If you need an easy solution  look for other answers  If you need the best performance  benchmark for yourself in the relevant execution environments   As others have said  the iteration through the array is probably the best way  but it has been proven that a decreasing while loop is the fastest way to iterate in JavaScript  So you may want to rewrite your code as follows   function contains a  obj        var i   a length      while  i--           if  a i      obj               return true                     return false      Of course  you may as well extend Array prototype   Array prototype contains   function obj        var i   this length      while  i--            if  this i      obj                return true                      return false      And now you can simply use the following   alert  1  2  3  contains 2         gt  true alert  1  2  3  contains  2          gt  false

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We use this snippet  works with objects  arrays  strings           function     name Object prototype inArray     description Extend Object prototype within inArray function        param  mix     needle       - Search-able needle     param  bool    searchInKey  - Search needle in keys         Object defineProperty Object prototype   inArray        value  function needle  searchInKey            var object   this           if  Object prototype toString call needle        object Object                   Object prototype toString call needle        object Array                 needle   JSON stringify needle                      return Object keys object  some function key                var value   object key                if  Object prototype toString call value        object Object                       Object prototype toString call value        object Array                     value   JSON stringify value                              if searchInKey                   if value     needle    key     needle                   return true                                 else                  if value     needle                       return true                                                         writable  true      configurable  true      enumerable  false       Usage   var a    one   first   two   second   foo   three   third     a inArray  first               true a inArray  foo                 false a inArray  foo   true          true - search by keys a inArray  three   third       true  var b     one    two    three    four    foo   val     b inArray  one              true b inArray  foo              false b inArray  foo   val        true b inArray   foo   val       false  var c    String   c inArray  S             true c inArray  s             false c inArray  2   true      true c inArray  20   true     false

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While array indexOf x   -1 is the most concise way to do this  and has been supported by non-Internet nbsp Explorer browsers for over decade      it is not O 1   but rather O N   which is terrible  If your array will not be changing  you can convert your array to a hashtable  then do table x    undefined or    undefined   Array prototype toTable   function         var t           this forEach function x  t x  true        return t      Demo   var toRemove    2 4  toTable     1 2 3 4 5  filter function x  return toRemove x    undefined      Unfortunately  while you can create an Array prototype contains to  freeze  an array and store a hashtable in this  cache in two lines  this would give wrong results if you chose to edit your array later  JavaScript has insufficient hooks to let you keep this state  unlike Python for example

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If you are using JavaScript 1 6 or later  Firefox 1 5 or later  you can use Array indexOf   Otherwise  I think you are going to end up with something similar to your original code

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Use indexOf    You can use the indexOf   method to check whether a given value or element exists in an array or not  The indexOf   method returns the index of the element inside the array if it is found  and returns -1 if it not found  Let s take a look at the following example    x000D   x000D  var fruits     Apple    Banana    Mango    Orange    Papaya    x000D  var a    Mango   x000D  checkArray a  fruits   x000D   x000D   x000D  function checkArray a  fruits    x000D       Check if a value exists in the fruits array x000D    if  fruits indexOf a      -1    x000D      return document write  true    x000D      else   x000D      return document write  false    x000D      x000D    x000D   x000D   x000D    Use include   Method  ES6 has introduced the includes   method to perform this task very easily  But  this method returns only true or false instead of index number    x000D   x000D  var fruits     Apple    Banana    Mango    Orange    Papaya    x000D  alert fruits includes  Banana        Outputs  true x000D  alert fruits includes  Coconut        Outputs  false x000D  alert fruits includes  Orange        Outputs  true x000D  alert fruits includes  Cherry        Outputs  false x000D   x000D   x000D    For further reference checkout here

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If you are using JavaScript 1 6 or later  Firefox 1 5 or later  you can use Array indexOf   Otherwise  I think you are going to end up with something similar to your original code

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indexOf maybe  but it s a  JavaScript extension to the ECMA-262 standard  as such it may not be present in other implementations of the standard    Example    1  2  3  indexOf 1    gt  0   foo    bar    baz   indexOf  bar     gt  1  1  2  3  indexOf 4    gt  -1   AFAICS Microsoft does not offer some kind of alternative to this  but you can add similar functionality to arrays in Internet Explorer  and other browsers that don t support indexOf  if you want to  as a quick Google search reveals  for example  this one

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Simple solution   ES6 Features   includes  method   let arr    1  2  3  2  3  2  3  4      arr includes 2     true    arr includes 93     false

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Here s a JavaScript 1 6 compatible implementation of Array indexOf   if   Array indexOf        Array indexOf      indexOf           function arr  obj  from                return arr indexOf obj  from                       function arr  obj  from        for IE6              var l   arr length                  i   from   parseInt  1   from     from  lt  0   l   0   10    0              i   i  lt  0   0   i              for    i  lt  l  i                      if  i in arr  amp  amp  arr i      obj                        return i                                              return -1

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indexOf maybe  but it s a  JavaScript extension to the ECMA-262 standard  as such it may not be present in other implementations of the standard    Example    1  2  3  indexOf 1    gt  0   foo    bar    baz   indexOf  bar     gt  1  1  2  3  indexOf 4    gt  -1   AFAICS Microsoft does not offer some kind of alternative to this  but you can add similar functionality to arrays in Internet Explorer  and other browsers that don t support indexOf  if you want to  as a quick Google search reveals  for example  this one

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A hopefully faster bidirectional indexOf   lastIndexOf alternative  2015  While the new method includes is very nice  the support is basically zero for now   It s long time that I was thinking of way to replace the slow indexOf lastIndexOf functions   A performant way has already been found  looking at the top answers  From those I chose the contains function posted by  Damir Zekic which should be the fastest one  But it also states that the benchmarks are from 2008 and so are outdated   I also prefer while over for  but for not a specific reason I ended writing the function with a for loop  It could be also done with a while --   I was curious if the iteration was much slower if I check both sides of the array while doing it  Apparently no  and so this function is around two times faster than the top voted ones  Obviously it s also faster than the native one  This in a real world environment  where you never know if the value you are searching is at the beginning or at the end of the array   When you know you just pushed an array with a value  using lastIndexOf remains probably the best solution  but if you have to travel through big arrays and the result could be everywhere  this could be a solid solution to make things faster   Bidirectional indexOf lastIndexOf  function bidirectionalIndexOf a  b  c  d  e     for c a length d c 1  c--         if a c   b  return c    or this c    b     if a e d-1-c   b  return e    or a e d-1-c    b       return -1      Usage bidirectionalIndexOf array  value      Performance test  http   jsperf com bidirectionalindexof  As test I created an array with 100k entries   Three queries  at the beginning  in the middle  amp  at the end of the array   I hope you also find this interesting and test the performance   Note  As you can see I slightly modified the contains function to reflect the indexOf  amp  lastIndexOf output  so basically true with the index and false with -1   That shouldn t harm it   The array prototype variant  Object defineProperty Array prototype  bidirectionalIndexOf   value function b c d e     for c this length d c 1  c--         if this c   b  return c    or this c    b     if this e d-1-c     b  return e    or this e d-1-c    b       return -1   writable false  enumerable false        Usage array bidirectionalIndexOf  value      The function can also be easily modified to return true or false or even the object  string or whatever it is   And here is the while variant   function bidirectionalIndexOf a  b  c  d     c a length  d c-1    while c--       if b   a c   return c      if b   a d-c   return d-c        return c       Usage bidirectionalIndexOf array  value      How is this possible   I think that the simple calculation to get the reflected index in an array is so simple that it s two times faster than doing an actual loop iteration   Here is a complex example doing three checks per iteration  but this is only possible with a longer calculation which causes the slowdown of the code   http   jsperf com bidirectionalindexof 2

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Simple solution for this requirement is using find    If you re having array of objects like below   var users     id   101   name   Choose one        id   102   name   shilpa     id   103   name   anita     id   104   name   admin     id   105   name   user       Then you can check whether the object with your value is already present or not  let data   users find object   gt  object  id        104      if data is null then no admin  else it will return the existing object like below    id   104   name   admin     Then you can find the index of that object in the array and replace the object using below code   let indexToUpdate   users indexOf data   let newObject    id   104   name   customer    users indexToUpdate    newObject   your new object console log users     you will get value like below    id   101   name   Choose one        id   102   name   shilpa     id   103   name   anita     id   104   name   customer     id   105   name   user       hope this will help anyone

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Use   function isInArray array  search        return array indexOf search   gt   0        Usage if isInArray my array   my value

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If you re working with ES6 You can use a set   function arrayHas  array  element         const s   new Set array       return s has element      This should be more performant than just about any other method

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You can also use this trick   var arrayContains   function object      return  serverList filter function currentObject        if  currentObject     object          return currentObject           else         return false             length  gt  0    true   false

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ECMAScript 7 introduces Array prototype includes   It can be used like this    1  2  3  includes 2      true  1  2  3  includes 4      false   It also accepts an optional second argument fromIndex    1  2  3  includes 3  3      false  1  2  3  includes 3  -1      true   Unlike indexOf  which uses Strict Equality Comparison  includes compares using SameValueZero equality algorithm  That means that you can detect if an array includes a NaN    1  2  NaN  includes NaN      true   Also unlike indexOf  includes does not skip missing indices   new Array 5  includes undefined      true   Currently it s still a draft but can be polyfilled to make it work on all browsers

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I looked through submitted answers and got that they only apply if you search for the object via reference  A simple linear search with reference object comparison    But lets say you don t have the reference to an object  how will you find the correct object in the array  You will have to go linearly and deep compare with each object  Imagine if the list is too large  and the objects in it are very big containing big pieces of text  The performance drops drastically with the number and size of the elements in the array   You can stringify objects and put them in the native hash table  but then you will have data redundancy remembering these keys cause JavaScript keeps them for  for i in obj   and you only want to check if the object exists or not  that is  you have the key   I thought about this for some time constructing a JSON Schema validator  and I devised a simple wrapper for the native hash table  similar to the sole hash table implementation  with some optimization exceptions which I left to the native hash table to deal with  It only needs performance benchmarking    All the details and code can be found on my blog  http   stamat wordpress com javascript-quickly-find-very-large-objects-in-a-large-array  I will soon post benchmark results    The complete solution works like this   var a     a  1    b    c   1 2  3 45  4 5     d    q  1   b    q  1   b  8   c  4     u   lol      e  2     var b     a  1     b    c   2 3  1      d    q  3  b    b  3       e  2     var c    Lorem Ipsum is simply dummy text of the printing and typesetting industry  Lorem Ipsum has been the industry s standard dummy text ever since the 1500s  when an unknown printer took a galley of type and scrambled it to make a type specimen book  It has survived not only five centuries  but also the leap into electronic typesetting  remaining essentially unchanged  It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages  and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum      var hc   new HashCache   a 3  b 2  c 5    a 15  b 2  c  foo        init   hc put  a 1  b 1     hc put  b 1  a 1     hc put true    hc put  true     hc put a    hc put c    hc put d    console log hc exists  true      console log hc exists a     console log hc exists c     console log hc exists  b 1  a 1      hc remove a    console log hc exists c

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If you are using JavaScript 1 6 or later  Firefox 1 5 or later  you can use Array indexOf   Otherwise  I think you are going to end up with something similar to your original code

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A hopefully faster bidirectional indexOf   lastIndexOf alternative  2015  While the new method includes is very nice  the support is basically zero for now   It s long time that I was thinking of way to replace the slow indexOf lastIndexOf functions   A performant way has already been found  looking at the top answers  From those I chose the contains function posted by  Damir Zekic which should be the fastest one  But it also states that the benchmarks are from 2008 and so are outdated   I also prefer while over for  but for not a specific reason I ended writing the function with a for loop  It could be also done with a while --   I was curious if the iteration was much slower if I check both sides of the array while doing it  Apparently no  and so this function is around two times faster than the top voted ones  Obviously it s also faster than the native one  This in a real world environment  where you never know if the value you are searching is at the beginning or at the end of the array   When you know you just pushed an array with a value  using lastIndexOf remains probably the best solution  but if you have to travel through big arrays and the result could be everywhere  this could be a solid solution to make things faster   Bidirectional indexOf lastIndexOf  function bidirectionalIndexOf a  b  c  d  e     for c a length d c 1  c--         if a c   b  return c    or this c    b     if a e d-1-c   b  return e    or a e d-1-c    b       return -1      Usage bidirectionalIndexOf array  value      Performance test  http   jsperf com bidirectionalindexof  As test I created an array with 100k entries   Three queries  at the beginning  in the middle  amp  at the end of the array   I hope you also find this interesting and test the performance   Note  As you can see I slightly modified the contains function to reflect the indexOf  amp  lastIndexOf output  so basically true with the index and false with -1   That shouldn t harm it   The array prototype variant  Object defineProperty Array prototype  bidirectionalIndexOf   value function b c d e     for c this length d c 1  c--         if this c   b  return c    or this c    b     if this e d-1-c     b  return e    or this e d-1-c    b       return -1   writable false  enumerable false        Usage array bidirectionalIndexOf  value      The function can also be easily modified to return true or false or even the object  string or whatever it is   And here is the while variant   function bidirectionalIndexOf a  b  c  d     c a length  d c-1    while c--       if b   a c   return c      if b   a d-c   return d-c        return c       Usage bidirectionalIndexOf array  value      How is this possible   I think that the simple calculation to get the reflected index in an array is so simple that it s two times faster than doing an actual loop iteration   Here is a complex example doing three checks per iteration  but this is only possible with a longer calculation which causes the slowdown of the code   http   jsperf com bidirectionalindexof 2

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OK  you can just optimise your code to get the result    There are many ways to do this which are cleaner and better  but I just wanted to get your pattern and apply to that using JSON stringify  just simply do something like this in your case   function contains a  obj        for  var i   0  i  lt  a length  i              if  JSON stringify a i       JSON stringify obj                 return true                      return false

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One-liner   function contains arr  x        return arr filter function elem    return elem    x    length  gt  0

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If you re working with ES6 You can use a set   function arrayHas  array  element         const s   new Set array       return s has element      This should be more performant than just about any other method

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Or this solution   Array prototype includes   function  object      return     this indexOf object

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Let s say you ve defined an array like so   const array    1  2  3  4    Below are three ways of checking whether there is a 3 in there  All of them return either true or false   Native Array method  since ES2016   compatibility table   array includes 3     true   As custom Array method  pre ES2016      Prefixing the method with     to avoid name clashes Object defineProperty Array prototype    includes     value  function  v    return this indexOf v      -1     array  includes 3     true   Simple function  const includes    a  v    gt  a indexOf v      -1 includes array  3     true

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If you are using JavaScript 1 6 or later  Firefox 1 5 or later  you can use Array indexOf   Otherwise  I think you are going to end up with something similar to your original code

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x000D   x000D      function countArray originalArray    x000D        x000D       var compressed       x000D          make a copy of the input array x000D       var copyArray   originalArray slice 0   x000D        x000D          first loop goes over every element x000D       for  var i   0  i  lt  originalArray length  i      x000D        x000D        var count   0   x000D           loop over every element in the copy and see if it s the same x000D        for  var w   0  w  lt  copyArray length  w      x000D         if  originalArray i     copyArray w     x000D             increase amount of times duplicate is found x000D          count    x000D             sets item to undefined x000D          delete copyArray w   x000D           x000D          x000D        x000D        if  count  gt  0    x000D         var a   new Object    x000D         a value   originalArray i   x000D         a count   count  x000D         compressed push a   x000D          x000D         x000D        x000D       return compressed  x000D         x000D       x000D         It should go something like this  x000D       x000D      var testArray   new Array  dog    dog    cat    buffalo    wolf    cat    tiger    cat    x000D      var newArray   countArray testArray   x000D      console log newArray   x000D   x000D   x000D

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Similar thing  Finds the first element by a  search lambda    Array prototype find   function search lambda      return this this map search lambda  indexOf true         Usage    1 3 4 5 8 3 5  find function item    return item   2    0      gt  4   Same in coffeescript   Array prototype find    search lambda  - gt     map search lambda  indexOf true

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One can use Set that has the method  has       x000D   x000D  function contains arr  obj    x000D        var proxy   new Set arr   x000D        if  proxy has obj   x000D          return true  x000D        else x000D          return false  x000D        x000D   x000D      var arr     Happy    New    Year    x000D      console log contains arr   Happy     x000D   x000D   x000D

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Use indexOf    You can use the indexOf   method to check whether a given value or element exists in an array or not  The indexOf   method returns the index of the element inside the array if it is found  and returns -1 if it not found  Let s take a look at the following example    x000D   x000D  var fruits     Apple    Banana    Mango    Orange    Papaya    x000D  var a    Mango   x000D  checkArray a  fruits   x000D   x000D   x000D  function checkArray a  fruits    x000D       Check if a value exists in the fruits array x000D    if  fruits indexOf a      -1    x000D      return document write  true    x000D      else   x000D      return document write  false    x000D      x000D    x000D   x000D   x000D    Use include   Method  ES6 has introduced the includes   method to perform this task very easily  But  this method returns only true or false instead of index number    x000D   x000D  var fruits     Apple    Banana    Mango    Orange    Papaya    x000D  alert fruits includes  Banana        Outputs  true x000D  alert fruits includes  Coconut        Outputs  false x000D  alert fruits includes  Orange        Outputs  true x000D  alert fruits includes  Cherry        Outputs  false x000D   x000D   x000D    For further reference checkout here

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I use the following   Array prototype contains   function  v        return this indexOf v   gt  -1     var a      foo    bar      a contains  foo       true a contains  fox       false

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If you are checking repeatedly for existence of an object in an array you should maybe look into   Keeping the array sorted at all times by doing insertion sort in your array  put new objects in on the right place   Make updating objects as remove sorted insert operation and Use a binary search lookup in your contains a  obj

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Object keys for getting all property names of the object and filter all values that exact or partial match with specified string   x000D   x000D  function filterByValue array  string      return array filter o   gt      Object keys o  some k   gt  o k  toLowerCase   includes string toLowerCase          const arrayOfObject        name   Paul     country   Canada          name   Lea     country   Italy          name   John     country   Italy       console log filterByValue arrayOfObject   lea          name   Lea   country   Italy    console log filterByValue arrayOfObject   ita          name   Lea   country   Italy     name   John   country   Italy    x000D   x000D   x000D   You can also filter by specific key such as  Object keys o  some k   gt  o country toLowerCase   includes string toLowerCase        Now you can just check array count after filtered to check value contains or not  Hope it s helpful

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Use lodash s some function   It s concise  accurate and has great cross platform support   The accepted answer does not even meet the requirements   Requirements  Recommend most concise and efficient way to find out if a JavaScript array contains an object   Accepted Answer     inArray   b   2      a   1     b   2     gt  -1   My recommendation     some    a   1     b   2      b   2    gt  true   Notes      inArray works fine for determining whether a scalar value exists in an array of scalars       inArray 2   1 2    gt  1       but the question clearly asks for an efficient way to determine if an object is contained in an array   In order to handle both scalars and objects  you could do this      isObject item       some ary  item       indexOf ary  item   gt  -1

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Using idnexOf   it is a good solution  but you should hide embedded implementation indexOf   function which returns -1 with   operator    function include arr obj         return     arr indexOf obj

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Solution that works in all modern browsers   function contains arr  obj      const stringifiedObj   JSON stringify obj      Cache our object to not call  JSON stringify  on every iteration   return arr some item   gt  JSON stringify item      stringifiedObj       Usage   contains   a  1    a  2     a  1       true   IE6  solution   function contains arr  obj      var stringifiedObj   JSON stringify obj    return arr some function  item        return JSON stringify item      stringifiedObj               some polyfill  not needed for IE9  if     some  in Array prototype       Array prototype some   function  tester  that   opt          for  var i   0  n   this length  i  lt  n  i            if  i in this  amp  amp  tester call that  this i   i  this   return true        return false           Usage   contains   a  1    a  2     a  1       true   Why to use JSON stringify   Array indexOf and Array includes  as well as most of the answers here  only compare by reference and not by value     a  1    a  2   includes  a  1       false  because  a  1  is a new object   Bonus  Non-optimized ES6 one-liner     a  1    a  2   some item   gt  JSON stringify item      JSON stringify  a  1       true     Note  Comparing objects by value will work better if the keys are in the same order  so to be safe you might sort the keys first with a package like this one  https   www npmjs com package sort-keys    Updated the contains function with a perf optimization  Thanks itinance for pointing it out

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Modern browsers have Array includes  which does exactly that and is widely supported by everyone except IE   x000D   x000D  console log   joe    jane    mary   includes  jane       true x000D   x000D   x000D   You can also use Array indexOf  which is less direct  but doesn t require polyfills for outdated browsers   x000D   x000D  console log   joe    jane    mary   indexOf  jane    gt   0     true x000D   x000D   x000D    Many frameworks also offer similar methods   jQuery    inArray value  array   fromIndex   Underscore js    contains array  value   also aliased as   include and   includes  Dojo Toolkit  dojo indexOf array  value   fromIndex  findLast   Prototype  array indexOf value  MooTools  array indexOf value  MochiKit  findValue array  value  MS Ajax  array indexOf value  Ext  Ext Array contains array  value  Lodash    includes array  value   from    is   contains prior 4 0 0  Ramda  R includes value  array   Notice that some frameworks implement this as a function  while others add the function to the array prototype

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As others have mentioned you can use Array indexOf  but it isn t available in all browsers  Here s the code from https   developer mozilla org en-US docs JavaScript Reference Global Objects Array indexOf to make it work the same in older browsers      indexOf is a recent addition to the ECMA-262 standard  as such it may   not be present in all browsers  You can work around this by inserting   the following code at the beginning of your scripts  allowing use of   indexOf in implementations which do not natively support it  This   algorithm is exactly the one specified in ECMA-262  5th edition    assuming Object  TypeError  Number  Math floor  Math abs  and Math max   have their original value    if   Array prototype indexOf        Array prototype indexOf   function  searchElement     fromIndex                 use strict           if  this    null                throw new TypeError                      var t   Object this           var len   t length  gt  gt  gt  0          if  len     0                return -1                    var n   0          if  arguments length  gt  1                n   Number arguments 1                if  n    n       shortcut for verifying if it s NaN                 n   0                else if  n    0  amp  amp  n    Infinity  amp  amp  n    -Infinity                    n    n  gt  0    -1    Math floor Math abs n                                    if  n  gt   len                return -1                    var k   n  gt   0   n   Math max len - Math abs n   0           for    k  lt  len  k                  if  k in t  amp  amp  t k      searchElement                    return k                                  return -1

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Performance  Today 2020 01 07 I perform tests on MacOs HighSierra 10 13 6 on Chrome v78 0 0  Safari v13 0 4 and Firefox v71 0 0 for 15 chosen solutions  Conclusions   solutions based on JSON  Set and surprisingly find  K N O  are slowest on all browsers the es6 includes  F  is fast only on chrome the solutions based on for  C D  and indexOf  G H  are quite-fast on all browsers on small and big arrays so probably they are best choice for efficient solution the solutions where index decrease during loop   B  is slower probably because the way of CPU cache works   I also run test for big array when searched element was on position 66  of array length  and solutions based on for  C D E  gives similar results   630 ops sec - but the E on safari and firefox was 10-20  slower than C and D    Results    Details  I perform 2 tests cases  for array with 10 elements  and array with 1 milion elements  In both cases we put searched element in the array middle    x000D   x000D  let log    name f    gt  console log    name   3-  f arr  s10      s7 -  f arr  s7     6-  f arr 6    s3 -  f arr  s3      x000D   x000D  let arr    1 2 3 4 5  s6   s7   s8   s9   s10    x000D    arr   new Array 1000000  fill 123   arr 500000  7  x000D   x000D  function A a  val    x000D      var i   -1  x000D      var n   a length  x000D      while  i   lt n    x000D         if  a i      val    x000D             return true  x000D           x000D        x000D      return false  x000D    x000D   x000D  function B a  val    x000D      var i   a length  x000D      while  i--    x000D         if  a i      val    x000D             return true  x000D           x000D        x000D      return false  x000D    x000D   x000D  function C a  val    x000D      for  var i   0  i  lt  a length  i      x000D          if  a i      val  return true  x000D        x000D      return false  x000D    x000D   x000D  function D a val  x000D    x000D      var len   a length  x000D      for var i   0   i  lt  len i    x000D        x000D          if a i      val  return true  x000D        x000D      return false  x000D     x000D   x000D  function E a  val     x000D    var n   a length-1  x000D    var t   n 2  x000D    for  var i   0  i  lt   t  i      x000D          if  a i      val    a n-i      val  return true  x000D      x000D    return false  x000D    x000D   x000D  function F a val    x000D   return a includes val   x000D    x000D   x000D  function G a val    x000D   return a indexOf val  gt  0  x000D    x000D   x000D  function H a val    x000D   return    a indexOf val   x000D    x000D   x000D  function I a  val    x000D    return a findIndex x  gt  x  val  gt  0  x000D    x000D   x000D  function J a val    x000D   return a some x  gt  x   val   x000D    x000D   x000D  function K a  val    x000D    const s   JSON stringify val   x000D    return a some x   gt  JSON stringify x      s   x000D    x000D   x000D  function L a val    x000D   return  a every x  gt  x   val   x000D    x000D   x000D  function M a  val    x000D    return   a find x  gt  x  val   x000D    x000D   x000D  function N a val    x000D   return a filter x  gt x   val  length  gt  0  x000D    x000D   x000D  function O a  val    x000D    return new Set a  has val   x000D    x000D   x000D  log  A  A   x000D  log  B  B   x000D  log  C  C   x000D  log  D  D   x000D  log  E  E   x000D  log  F  F   x000D  log  G  G   x000D  log  H  H   x000D  log  I  I   x000D  log  J  J   x000D  log  K  K   x000D  log  L  L   x000D  log  M  M   x000D  log  N  N   x000D  log  O  O   x000D  This shippet only presents functions used in performance tests - it not perform tests itself  x000D   x000D   x000D    Array small - 10 elements  You can perform tests in your machine HERE    Array big - 1 000 000 elements  You can perform tests in your machine HERE

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Simple solution for this requirement is using find    If you re having array of objects like below   var users     id   101   name   Choose one        id   102   name   shilpa     id   103   name   anita     id   104   name   admin     id   105   name   user       Then you can check whether the object with your value is already present or not  let data   users find object   gt  object  id        104      if data is null then no admin  else it will return the existing object like below    id   104   name   admin     Then you can find the index of that object in the array and replace the object using below code   let indexToUpdate   users indexOf data   let newObject    id   104   name   customer    users indexToUpdate    newObject   your new object console log users     you will get value like below    id   101   name   Choose one        id   102   name   shilpa     id   103   name   anita     id   104   name   customer     id   105   name   user       hope this will help anyone

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Adding a unique item to a another list  searchResults                                          name   Hello                       artist   Selana                       album   Riga                       id  1                                                           name   Hello s                       artist   Selana G                       album   Riga1                       id  2                                                           name   Hello2                       artist   Selana                       album   Riga11                       id  3                                               playlistTracks                                    name   Hello                   artist   Mamunuus                   album   Riga                   id  4                                                   name   Hello s                   artist   Mamunuus G                   album   Riga1                   id  2                                                   name   Hello2                   artist   Mamunuus New                   album   Riga11                   id  3                                             playlistName   New PlayListTrack                            Adding an unique track in the playList     addTrack   track   gt          if playlistTracks find savedTrack   gt  savedTrack id     track id             return                playlistTracks push track          this setState           playlistTracks

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It has one parameter  an array numbers of objects  Each object in the array has two integer properties denoted by x and y  The function must return a count of all such objects in the array that satisfy numbers x    numbers y   x000D   x000D  var numbers       x  1  y  1    x000D                    x  2  y  3    x000D                    x  3  y  3    x000D                    x  3  y  4    x000D                    x  4  y  5      x000D  var count   0   x000D  var n   numbers length  x000D  for  var i  0 i lt n i    x000D    x000D    if numbers i  x  numbers i  y  x000D       count  1   x000D    x000D   x000D  alert count   x000D   x000D   x000D

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Extending the JavaScript Array object is a really bad idea because you introduce new properties  your custom methods  into for-in loops which can break existing scripts  A few years ago the authors of the Prototype library had to re-engineer their library implementation to remove just this kind of thing   If you don t need to worry about compatibility with other JavaScript running on your page  go for it  otherwise  I d recommend the more awkward  but safer free-standing function solution

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Modern browsers have Array includes  which does exactly that and is widely supported by everyone except IE   x000D   x000D  console log   joe    jane    mary   includes  jane       true x000D   x000D   x000D   You can also use Array indexOf  which is less direct  but doesn t require polyfills for outdated browsers   x000D   x000D  console log   joe    jane    mary   indexOf  jane    gt   0     true x000D   x000D   x000D    Many frameworks also offer similar methods   jQuery    inArray value  array   fromIndex   Underscore js    contains array  value   also aliased as   include and   includes  Dojo Toolkit  dojo indexOf array  value   fromIndex  findLast   Prototype  array indexOf value  MooTools  array indexOf value  MochiKit  findValue array  value  MS Ajax  array indexOf value  Ext  Ext Array contains array  value  Lodash    includes array  value   from    is   contains prior 4 0 0  Ramda  R includes value  array   Notice that some frameworks implement this as a function  while others add the function to the array prototype

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Either use Array indexOf Object    With ECMA 7 one can use the Array includes Object    With ECMA 6 you can use Array find FunctionName  where FunctionName is a user  defined function to search for the object in the array   Hope this helps

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I use the following   Array prototype contains   function  v        return this indexOf v   gt  -1     var a      foo    bar      a contains  foo       true a contains  fox       false

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Update from 2019  This answer is from 2008  11 years old   and is not relevant for modern JS usage  The promised performance improvement was based on a benchmark done in browsers of that time  It might not be relevant to modern JS execution contexts  If you need an easy solution  look for other answers  If you need the best performance  benchmark for yourself in the relevant execution environments   As others have said  the iteration through the array is probably the best way  but it has been proven that a decreasing while loop is the fastest way to iterate in JavaScript  So you may want to rewrite your code as follows   function contains a  obj        var i   a length      while  i--           if  a i      obj               return true                     return false      Of course  you may as well extend Array prototype   Array prototype contains   function obj        var i   this length      while  i--            if  this i      obj                return true                      return false      And now you can simply use the following   alert  1  2  3  contains 2         gt  true alert  1  2  3  contains  2          gt  false

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In Addition to what others said  if you don t have a reference of the object which you want to search in the array  then you can do something like this   let array    1  2  3  4    key    value      array some  element    gt  JSON stringify element      JSON stringify   key    value        true  array some  element    gt  JSON stringify element      JSON stringify         true   Array some returns true if any element matches the given condition and returns false if none of the elements matches the given condition

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Surprised that this question still doesn t have latest syntax added  adding my 2 cents   Let s say we have array of Objects arrObj and we want to search obj in it   Array prototype indexOf -   returns index or -1  is generally used for finding index of element in array  This can also be used for searching object but only works if you are passing reference to same object   let obj     name   Sumer   age  36    let arrObj    obj    name   Kishor   age  46      name   Rupen   age  26       console log arrObj indexOf obj      0 console log arrObj indexOf   name   Sumer   age  36        -1  console log  1  3  5  2  indexOf 2      3   Array prototype includes -   returns true or false   console log arrObj includes obj       true console log arrObj includes   name   Sumer   age  36        false  console log  1  3  5  2  includes 2      true   Array prototype find -   takes callback  returns first value object that returns true in CB    console log arrObj find e   gt  e age  gt  40         name   Kishor   age  46   console log arrObj find e   gt  e age  gt  40        name   Kishor   age  46    console log  1  3  5  2  find e   gt  e  gt  2      3   Array prototype findIndex -   takes callback  returns index of first value object that returns true in CB    console log arrObj findIndex e   gt  e age  gt  40       1 console log arrObj findIndex e   gt  e age  gt  40      1  console log  1  3  5  2  findIndex e   gt  e  gt  2      1   Since find and findIndex takes a callback  we can be fetch any object even if we don t have the reference  from array by creatively setting the true condition

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I was working on a project that I needed a functionality like python set which removes all duplicates values and returns a new list  so I wrote this function maybe useful to someone  function set arr        var res           for  var i   0  i  lt  arr length  i              if  res indexOf arr i       -1                res push arr i                        return res

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ECMAScript 6 has an elegant proposal on find      The find method executes the callback function once for each element   present in the array until it finds one where callback returns a true   value  If such an element is found  find immediately returns the value   of that element  Otherwise  find returns undefined  callback is   invoked only for indexes of the array which have assigned values  it   is not invoked for indexes which have been deleted or which have never   been assigned values    Here is the MDN documentation on that   The find functionality works like this   function isPrime element  index  array        var start   2      while  start  lt   Math sqrt element             if  element   start    lt  1  return false            return  element  gt  1      console log   4  6  8  12  find isPrime        Undefined  not found console log   4  5  8  12  find isPrime        5   You can use this in ECMAScript 5 and below by defining the function   if   Array prototype find      Object defineProperty Array prototype   find         enumerable  false      configurable  true      writable  true      value  function predicate          if  this    null            throw new TypeError  Array prototype find called on null or undefined                  if  typeof predicate      function             throw new TypeError  predicate must be a function                  var list   Object this         var length   list length  gt  gt  gt  0        var thisArg   arguments 1         var value         for  var i   0  i  lt  length  i              if  i in list              value   list i             if  predicate call thisArg  value  i  list                 return value                                      return undefined

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function inArray elem array        var len   array length      for var i   0   i  lt  len i                  if array i     elem  return i             return -1       Returns array index if found  or -1 if not found

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As others have mentioned you can use Array indexOf  but it isn t available in all browsers  Here s the code from https   developer mozilla org en-US docs JavaScript Reference Global Objects Array indexOf to make it work the same in older browsers      indexOf is a recent addition to the ECMA-262 standard  as such it may   not be present in all browsers  You can work around this by inserting   the following code at the beginning of your scripts  allowing use of   indexOf in implementations which do not natively support it  This   algorithm is exactly the one specified in ECMA-262  5th edition    assuming Object  TypeError  Number  Math floor  Math abs  and Math max   have their original value    if   Array prototype indexOf        Array prototype indexOf   function  searchElement     fromIndex                 use strict           if  this    null                throw new TypeError                      var t   Object this           var len   t length  gt  gt  gt  0          if  len     0                return -1                    var n   0          if  arguments length  gt  1                n   Number arguments 1                if  n    n       shortcut for verifying if it s NaN                 n   0                else if  n    0  amp  amp  n    Infinity  amp  amp  n    -Infinity                    n    n  gt  0    -1    Math floor Math abs n                                    if  n  gt   len                return -1                    var k   n  gt   0   n   Math max len - Math abs n   0           for    k  lt  len  k                  if  k in t  amp  amp  t k      searchElement                    return k                                  return -1

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This may be a detailed and easy solution     plain array var arr     a    b    c    var check   arr includes  a    console log check     returns true if  check          value exists in array      write some codes       array with objects var arr            x  a   y  b           x  p   y  q            if you want to check if x  p  exists in arr var check   arr filter function  elm       if  elm x     p                return elm     returns length   1  object exists in array                or y  q  exists in arr var check   arr filter function  elm       if  elm y     q                return elm     returns length   1  object exists in array                if you want to check  if the entire object  x  p   y  q   exists in arr var check   arr filter function  elm       if  elm x     p   amp  amp  elm y     q                return elm     returns length   1  object exists in array                in all cases console log check length      returns 1  if  check length  gt  0          returns true       object exists in array      write some codes

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Just another option     usage  if     a   b   c   d   contains  b             Array prototype contains   function value       for  var key in this          if  this key      value  return true      return false      Be careful because overloading javascript array objects with custom methods can disrupt the behavior of other javascripts  causing unexpected behavior

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If you are checking repeatedly for existence of an object in an array you should maybe look into   Keeping the array sorted at all times by doing insertion sort in your array  put new objects in on the right place   Make updating objects as remove sorted insert operation and Use a binary search lookup in your contains a  obj

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Use   function isInArray array  search        return array indexOf search   gt   0        Usage if isInArray my array   my value

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Here s a JavaScript 1 6 compatible implementation of Array indexOf   if   Array indexOf        Array indexOf      indexOf           function arr  obj  from                return arr indexOf obj  from                       function arr  obj  from        for IE6              var l   arr length                  i   from   parseInt  1   from     from  lt  0   l   0   10    0              i   i  lt  0   0   i              for    i  lt  l  i                      if  i in arr  amp  amp  arr i      obj                        return i                                              return -1

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Either use Array indexOf Object    With ECMA 7 one can use the Array includes Object    With ECMA 6 you can use Array find FunctionName  where FunctionName is a user  defined function to search for the object in the array   Hope this helps

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function inArray elem array        var len   array length      for var i   0   i  lt  len i                  if array i     elem  return i             return -1       Returns array index if found  or -1 if not found

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x000D   x000D      function countArray originalArray    x000D        x000D       var compressed       x000D          make a copy of the input array x000D       var copyArray   originalArray slice 0   x000D        x000D          first loop goes over every element x000D       for  var i   0  i  lt  originalArray length  i      x000D        x000D        var count   0   x000D           loop over every element in the copy and see if it s the same x000D        for  var w   0  w  lt  copyArray length  w      x000D         if  originalArray i     copyArray w     x000D             increase amount of times duplicate is found x000D          count    x000D             sets item to undefined x000D          delete copyArray w   x000D           x000D          x000D        x000D        if  count  gt  0    x000D         var a   new Object    x000D         a value   originalArray i   x000D         a count   count  x000D         compressed push a   x000D          x000D         x000D        x000D       return compressed  x000D         x000D       x000D         It should go something like this  x000D       x000D      var testArray   new Array  dog    dog    cat    buffalo    wolf    cat    tiger    cat    x000D      var newArray   countArray testArray   x000D      console log newArray   x000D   x000D   x000D

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I looked through submitted answers and got that they only apply if you search for the object via reference  A simple linear search with reference object comparison    But lets say you don t have the reference to an object  how will you find the correct object in the array  You will have to go linearly and deep compare with each object  Imagine if the list is too large  and the objects in it are very big containing big pieces of text  The performance drops drastically with the number and size of the elements in the array   You can stringify objects and put them in the native hash table  but then you will have data redundancy remembering these keys cause JavaScript keeps them for  for i in obj   and you only want to check if the object exists or not  that is  you have the key   I thought about this for some time constructing a JSON Schema validator  and I devised a simple wrapper for the native hash table  similar to the sole hash table implementation  with some optimization exceptions which I left to the native hash table to deal with  It only needs performance benchmarking    All the details and code can be found on my blog  http   stamat wordpress com javascript-quickly-find-very-large-objects-in-a-large-array  I will soon post benchmark results    The complete solution works like this   var a     a  1    b    c   1 2  3 45  4 5     d    q  1   b    q  1   b  8   c  4     u   lol      e  2     var b     a  1     b    c   2 3  1      d    q  3  b    b  3       e  2     var c    Lorem Ipsum is simply dummy text of the printing and typesetting industry  Lorem Ipsum has been the industry s standard dummy text ever since the 1500s  when an unknown printer took a galley of type and scrambled it to make a type specimen book  It has survived not only five centuries  but also the leap into electronic typesetting  remaining essentially unchanged  It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages  and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum      var hc   new HashCache   a 3  b 2  c 5    a 15  b 2  c  foo        init   hc put  a 1  b 1     hc put  b 1  a 1     hc put true    hc put  true     hc put a    hc put c    hc put d    console log hc exists  true      console log hc exists a     console log hc exists c     console log hc exists  b 1  a 1      hc remove a    console log hc exists c

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By no means the best  but I was just getting creative and adding to the repertoire  Do not use this  x000D   x000D  Object defineProperty Array prototype   exists       value  function element  index         var index   index    0      return index     this length   -1   this index      element   index   this exists element    index              Outputs 1 console log   one    two   exists  two         Outputs -1 console log   one    two   exists  three      console log   one    two    three    four   exists  four     x000D   x000D   x000D

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use Array prototype includes for example   x000D   x000D  const fruits     coconut    banana    apple    const doesFruitsHaveCoconut   fruits includes  coconut     true  console log doesFruitsHaveCoconut  x000D   x000D   x000D   maybe read this documentation from MDN  https   developer mozilla org en-US docs Web JavaScript Reference Global Objects Array includes

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Similar thing  Finds the first element by a  search lambda    Array prototype find   function search lambda      return this this map search lambda  indexOf true         Usage    1 3 4 5 8 3 5  find function item    return item   2    0      gt  4   Same in coffeescript   Array prototype find    search lambda  - gt     map search lambda  indexOf true

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One can use Set that has the method  has       x000D   x000D  function contains arr  obj    x000D        var proxy   new Set arr   x000D        if  proxy has obj   x000D          return true  x000D        else x000D          return false  x000D        x000D   x000D      var arr     Happy    New    Year    x000D      console log contains arr   Happy     x000D   x000D   x000D

[javascript] How do I check if an array includes a value in JavaScript?

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