Determine whether an array contains a value

Question

I need to determine if a value exists in an array   I am using the following function   Array prototype contains   function obj        var i   this length      while  i--            if  this i     obj                return true                      return false      The above function always returns false   The array values and the function call is as below   arrValues     Sam   Great    Sample    High   alert arrValues contains  Sam

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My little contribution   function isInArray array  search        return array indexOf search   gt   0       usage if isInArray my array   my value

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Wow  there are a lot of great answers to this question    I didn t see one that takes a reduce approach so I ll add it in   var searchForValue    pig    var valueIsInArray     horse    cat    dog   reduce function previous  current       return previous    searchForValue     current   true   false     false    console log  The value      searchForValue      is in the array      valueIsInArray     Here s a fiddle of it in action

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Since ECMAScript6  one can use Set   var myArray     A    B    C    var mySet   new Set myArray   var hasB   mySet has  B       true var hasZ   mySet has  Z       false

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jQuery has a utility function for this     inArray value  array    Returns index of value in array  Returns -1 if array does not contain value   See also How do I check if an array includes an object in JavaScript

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function setFound        var l   arr length  textBox1   document getElementById  text1        for var i 0  i lt l i               if arr i   searchele         textBox1  value    Found         return                   textBox1  value    Not Found   return         This program checks whether the given element is found or not  Id   text1 represents id of textbox and searchele represents element to be   searched  got fron user   if you want index  use i value

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This is generally what the indexOf   method is for  You would say   return arrValues indexOf  Sam    gt  -1

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Array prototype includes    In ES2016  there is Array prototype includes        The includes   method determines whether an array includes a certain element  returning true or false as appropriate    Example    Sam    Great    Sample    High   includes  Sam       true   Support  According to kangax and MDN  the following platforms are supported    Chrome 47 Edge 14 Firefox 43 Opera 34 Safari 9 Node 6   Support can be expanded using Babel  using babel-polyfill  or core-js  MDN also provides a polyfill   if      includes      Array prototype includes   function searchElement     fromIndex            use strict       var O   Object this       var len   parseInt O length     0      if  len     0          return false            var n   parseInt arguments 1      0      var k      if  n  gt   0          k   n        else         k   len   n        if  k  lt  0   k   0             var currentElement      while  k  lt  len          currentElement   O k         if  searchElement     currentElement              searchElement     searchElement  amp  amp  currentElement     currentElement             return true                k              return false

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The answer provided didn t work for me  but it gave me an idea   Array prototype contains   function obj                return  this join       indexOf obj   gt  -1          It isn t perfect because items that are the same beyond the groupings could end up matching   Such as my example  var c     var d     function a         var e    1       var f    2       c 0      1   1        c 1      2   2        c 2      3   3        d 0     document getElementById  g   value document getElementById  h   value        document getElementById  i   value   c join           document getElementById  j   value   d join           document getElementById  b   value   c contains d       When I call this function with the  g  and  h  fields containing 1 and 2 respectively  it still finds it because the resulting string from the join is   1 1 2 2 3 3  Since it is doubtful in my situation that I will come across this type of situation  I m using this   I thought I would share incase someone else couldn t make the chosen answer work either

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You can use   indexOf method or if you don t want to include whole Underscore js library in your app  you can have a look how they did it and extract necessary code         indexOf   function array  item  isSorted        if  array    null  return -1      var i   0  l   array length      if  isSorted          if  typeof isSorted     number             i    isSorted  lt  0   Math max 0  l   isSorted    isSorted           else           i     sortedIndex array  item           return array i      item   i   -1                    if  nativeIndexOf  amp  amp  array indexOf     nativeIndexOf  return array indexOf item  isSorted       for    i  lt  l  i    if  array i      item  return i      return -1

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I prefer simplicity   var days    1  2  3  4  5   if   2 in days    console log  weekday

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If you have access to ECMA 5 you can use the some method   MDN SOME Method Link  arrValues     Sam   Great    Sample    High     function namePresent name     return name     this toString         Note     namePresent requires  toString   method to coerce primitive value    i e  String  0   S   1   a   2   m   length  3    PrimitiveValue     Sam      into     Sam   arrValues some namePresent   Sam      gt  true    If you have access to ECMA 6 you can use the includes method   MDN INCLUDES Method Link  arrValues     Sam   Great    Sample    High     arrValues includes  Sam      gt  true

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The simplest solution for a contains function  would be a function that looks like this    var contains   function  haystack  needle        return    haystack indexOf needle       Ideally  you wouldn t make this a stand-alone function  though  but part of a helper library    var helper        helper array         contains   function  haystack  needle            return    haystack indexOf needle                        Now  if you happen to be one of those unlucky people who still needs to support IE lt 9 and thus can t rely on indexOf  you could use this polyfill  which I got from the MDN    if   Array prototype indexOf      Array prototype indexOf   function searchElement  fromIndex        var k      if  this    null          throw new TypeError   this  is null or not defined              var o   Object this       var len   o length  gt  gt  gt  0      if  len     0          return -1            var n    fromIndex    0       if  Math abs n      Infinity          n   0            if  n  gt   len          return -1            k   Math max n  gt   0   n   len - Math abs n   0       while  k  lt  len          if  k in o  amp  amp  o k      searchElement            return k                k              return -1

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Given the implementation of indexOf for IE  as described by eyelidlessness    Array prototype contains   function obj        return this indexOf obj   gt  -1

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Using array  map function that executes a function for every value in an array seems cleanest to me     Ref  Array prototype map    This method can work well both for simple arrays and for arrays of objects where you need to see if a key value exists in an array of objects   function inArray myArray myValue       var inArray   false      myArray map function key           if  key     myValue               inArray true                        return inArray      var anArray    2 4 6 8  console log inArray anArray  8       returns true console log inArray anArray  1       returns false  function inArrayOfObjects myArray myValue objElement       var inArray   false      myArray map function arrayObj           if  arrayObj objElement      myValue                inArray true                        return inArray      var objArray     id 4 value  foo    id 5 value  bar    console log inArrayOfObjects objArray  4   id        returns true console log inArrayOfObjects objArray   bar    value        returns true console log inArrayOfObjects objArray  1   id        returns false

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It s almost always safer to use a library like lodash simply because of all the issues with cross-browser compatibilities and efficiency   Efficiency because you can be guaranteed that at any given time  a hugely popular library like underscore will have the most efficient method of accomplishing a utility function like this     includes  1  2  3   3      returns true   If you re concerned about the bulk that s being added to your application by including the whole library  know that you can include functionality separately   var includes   require  lodash collections includes        NOTICE  With older versions of lodash  this was   contains   rather than   includes

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tl dr   function includes k      for var i 0  i  lt  this length  i         if  this i      k      this i      this i   amp  amp  k     k            return true              return false      Example   x000D   x000D  function includes k    x000D    for var i 0  i  lt  this length  i     x000D      if  this i      k      this i      this i   amp  amp  k     k      x000D        return true  x000D        x000D      x000D    return false  x000D    x000D   x000D  function log msg   x000D        out   append   lt div gt     msg     lt  div gt       x000D    x000D   x000D  var arr    1   2   NaN  true   x000D  arr includes   includes  x000D   x000D  log  var arr    1   2   NaN  true      x000D  log   lt br  gt     x000D  log  arr includes 1       arr includes 1    x000D  log  arr includes 2       arr includes 2    x000D  log  arr includes  2        arr includes  2     x000D  log  arr includes NaN       arr includes NaN    x000D  log  arr includes true       arr includes true    x000D  log  arr includes false       arr includes false    x000D   out  x000D    font-family monospace  x000D    x000D   lt script src  https   ajax googleapis com ajax libs jquery 2 1 1 jquery min js  gt  lt  script gt  x000D   lt div id out gt  lt  div gt  x000D   x000D   x000D    Longer Answer  I know this question isn t really about whether or not to extend built-in objects  but the attempt of the OP and the comments on this answer highlight that debate  My comment from Feb 12   13 cites an article that outlines this debate really well  however that link broke and I can t edit the original comment because too much time has passed  so I include it here   If you re looking to extend the built-in Array object with a contains method  probably the best and most responsible way to do this would be to use this polyfill from MDN   See also this section of the MDN article on Prototypical inheritance  which explains that  The only good reason for extending a built-in prototype is to backport the features of newer JavaScript engines  for example Array forEach  etc     if   Array prototype includes      Array prototype includes   function searchElement     fromIndex            use strict       var O   Object this       var len   parseInt O length     0      if  len     0          return false            var n   parseInt arguments 1      0      var k      if  n  gt   0          k   n        else         k   len   n        if  k  lt  0   k   0             var currentElement      while  k  lt  len          currentElement   O k         if  searchElement     currentElement              searchElement     searchElement  amp  amp  currentElement     currentElement             return true                k              return false           Don t want strict equality  or want to choose   function includes k  strict      strict   strict     false     default is true      strict     strict     default is false   for var i 0  i  lt  this length  i         if   this i      k  amp  amp  strict               this i     k  amp  amp   strict              this i      this i   amp  amp  k     k                return true              return false

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var contains   function needle           Per spec  the way to identify NaN is that it is not equal to itself     var findNaN   needle     needle      var indexOf       if  findNaN  amp  amp  typeof Array prototype indexOf      function             indexOf   Array prototype indexOf        else           indexOf   function needle                var i   -1  index   -1               for i   0  i  lt  this length  i                      var item   this i                    if  findNaN  amp  amp  item     item     item     needle                        index   i                      break                                               return index                        return indexOf call this  needle   gt  -1       You can use it like this   var myArray    0 1 2       needle   1      index   contains call myArray  needle      true   CodePen validation usage

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Another option would be to use Array some  if available  in the following way   Array prototype contains   function obj      return this some  function e   return e     obj          The anonymous function passed to Array some will return true if and only if there is an element in the array that is identical to obj  Absent such an element  the function will not return true for any of the elements of the array  so Array some will return false as well

[javascript] Determine whether an array contains a value

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