Best way to find if an item is in a JavaScript array

Question

What is the best way to find if an object is in an array   This is the best way I know    x000D   x000D  function include arr  obj    x000D    for  var i   0  i  lt  arr length  i      x000D      if  arr i     obj  return true  x000D      x000D    x000D   x000D  console log include  1  2  3  4   3       true x000D  console log include  1  2  3  4   6       undefined x000D   x000D   x000D

User · Answer

If you are using jQuery      inArray 5   5     8    9    10   10            For more information  http   api jquery com jQuery inArray

User · Answer

First  implement indexOf in JavaScript for browsers that don t already have it  For example  see Erik Arvidsson s array extras  also  the associated blog post   And then you can use indexOf without worrying about browser support  Here s a slightly optimised version of his indexOf implementation   if   Array prototype indexOf        Array prototype indexOf   function  obj  fromIndex            if  fromIndex    null                fromIndex   0            else if  fromIndex  lt  0                fromIndex   Math max 0  this length   fromIndex                     for  var i   fromIndex  j   this length  i  lt  j  i                  if  this i      obj                  return i                    return -1             It s changed to store the length so that it doesn t need to look it up every iteration  But the difference isn t huge  A less general purpose function might be faster   var include   Array prototype indexOf       function arr  obj    return arr indexOf obj      -1          function arr  obj            for var i   -1  j   arr length    i  lt  j               if arr i      obj  return true          return false           I prefer using the standard function and leaving this sort of micro-optimization for when it s really needed  But if you re keen on micro-optimization I adapted the benchmarks that roosterononacid linked to in the comments  to benchmark searching in arrays  They re pretty crude though  a full investigation would test arrays with different types  different lengths and finding objects that occur in different places

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has obj   assuming  indexOf   is implemented    Object defineProperty  Array prototype  has         value function o  flag       if  flag     undefined            return this indexOf o      -1        else        only for raw js object         for var v in this                if  JSON stringify this v       JSON stringify o   return true                    return false                                       writable false         enumerable false          do not make Array prototype has function       because you ll add an enumerable element in every array and js is broken     use like            22   a    prop  x    has 12     false   a   b   has  a       true   1  a 1   has  a 1  1     true  1  a 1   has  a 1      false   the use of 2nd arg  flag  forces  comparation by value instead of reference    comparing raw objects    o1  has o2 true     true if every level value is same

User · Answer

Here s some meta-knowledge for you - if you want to know what you can do with an Array  check the documentation - here s the Array page for Mozilla  https   developer mozilla org en-US docs JavaScript Reference Global Objects Array  There you ll see reference to indexOf  added in Javascript 1 6

User · Answer

A robust way to check if an object is an array in javascript is detailed here   Here are two functions from the xa js framework which I attach to a utils         container     These should help you properly detect arrays   var utils               utils isArray       Best guess if object is an array      utils isArray   function obj            do an instanceof check first      if  obj instanceof Array             return true                 then check for obvious falses      if  typeof obj      object              return false              if  utils type obj       array              return true              return false              utils type       Attempt to ascertain actual object type      utils type   function obj        if  obj     null    typeof obj      undefined             return String  obj             return Object prototype toString call obj           replace    object   a-zA-Z          1   toLowerCase         If you then want to check if an object is in an array  I would also include this code          Adding hasOwnProperty method if needed      if  typeof Object prototype hasOwnProperty      function         Object prototype hasOwnProperty   function  prop            var type   utils type this           type   type charAt 0  toUpperCase     type substr 1           return this prop      undefined              amp  amp  this prop      window type  prototype prop              And finally this in array function   function in array  needle  haystack  strict        var key       if  strict            for  key in haystack                if   haystack hasOwnProperty key   continue               if  haystack key      needle                    return true                                else           for  key in haystack                if   haystack hasOwnProperty key   continue               if  haystack key     needle                    return true                                     return false

User · Answer

If the array is unsorted  there isn t really a better way  aside from using the above-mentioned indexOf  which I think amounts to the same thing    If the array is sorted  you can do a binary search  which works like this    Pick the middle element of the array  Is the element you re looking for bigger than the element you picked   If so  you ve eliminated the bottom half of the array   If it isn t  you ve eliminated the top half  Pick the middle element of the remaining half of the array  and continue as in step 2  eliminating halves of the remaining array   Eventually you ll either find your element or have no array left to look through    Binary search runs in time proportional to the logarithm of the length of the array  so it can be much faster than looking at each individual element

User · Answer

It depends on your purpose  If you program for the Web  avoid indexOf  it isn t supported by Internet nbsp Explorer nbsp 6  lot of them still used    or do conditional use   if  yourArray indexOf     undefined  result   yourArray indexOf target   else result   customSlowerSearch yourArray  target     indexOf is probably coded in native code  so it is faster than anything you can do in JavaScript  except binary search dichotomy if the array is appropriate   Note  it is a question of taste  but I would do a return false  at the end of your routine  to return a true Boolean

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As of ECMAScript 2016 you can use includes   arr includes obj    If you want to support IE or other older browsers  function include arr obj        return  arr indexOf obj     -1      EDIT  This will not work on IE6  7 or 8 though  The best workaround is to define it yourself if it s not present   Mozilla s  ECMA-262  version     if   Array prototype indexOf                Array prototype indexOf   function searchElement     fromIndex                     quot use strict quot         if  this     void 0    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  0                n   Number arguments 1           if  n     n           n   0         else if  n     0  amp  amp  n      1   0   amp  amp  n     - 1   0            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              Daniel James s version   if   Array prototype indexOf       Array prototype indexOf   function  obj  fromIndex         if  fromIndex    null             fromIndex   0         else if  fromIndex  lt  0             fromIndex   Math max 0  this length   fromIndex               for  var i   fromIndex  j   this length  i  lt  j  i               if  this i      obj               return i              return -1             roosteronacid s version   Array prototype hasObject         Array indexOf   function  o            var l   this length   1       while  l -  1                  if  this l - 1      o                          return true                         return false         function  o            return  this indexOf o      -1

[javascript] Best way to find if an item is in a JavaScript array?

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