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 < a.length; i++) {
        if (a[i] === obj) {
            return true;
        }
    }
    return false;
}

Is there a better and more concise way to accomplish this?

This is very closely related to Stack Overflow question Best way to find an item in a JavaScript Array? which addresses finding objects in an array using indexOf.

just tested: your way is actually the fastest for across browsers: jsperf.com/find-element-in-obj-vs-array/2 (apart from pre-saving a.length in a variable) while using indexOf (as in $.inArray) is much slower — Jörn Berkefeld
– Jörn Berkefeld, Commented Jul 2, 2012 at 11:56
many have replied that the Array#indexOf is your best choice here. But if you want something that can be correctly cast to Boolean, use this: ~[1,2,3].indexOf(4) will return 0 which will evaluate as false, whereas ~[1,2,3].indexOf(3) will return -3 which will evaluate as true. — lordvlad
– lordvlad, Commented Oct 2, 2013 at 7:59
~ is not what you want to use to convert to a boolean, for that you need !. But in this case you want to check equality with -1, s o the function might endreturn [1,2,3].indexOf(3) === -1; ~ is a binary not, it will invert each bit of the value individually. — mcfedr
– mcfedr, Commented Jun 20, 2014 at 12:49
@Iordvlad [1,2,3].indexOf(4) will actually return -1. As @mcfedr pointed out, ~ is the bitwise-NOT operator, see ES5 11.4.8. Thing is, since the binary representation of -1 consists of only 1's, it's complement is 0, which evaluates as false. The complement of any other number will be non-zero, hence true. So, ~ works just fine and is often used in conjunction with indexOf. — mknecht
– mknecht, Commented Mar 14, 2015 at 5:35
The title is misleading. Where is the [[1,2],[3,4]].includes([3,4]) ? — mplungjan
– mplungjan, Commented Apr 2, 2017 at 9:20

Tiago Bértolo · Accepted Answer · 2022-08-14 20:37:28Z

-1

The fastest method in Javascript to find if an array contains a value is this:

function existsInArrayForIgnoreDataType(arr, targetElem) {
  for (let i = 0; i < arr.length; i++) {
    if (arr[i] == targetElem) return true
  }
  return false
 }

You can find the complete study I did here.

answered Aug 14, 2022 at 20:37

Tiago Bértolo

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1 Comment

surge10 Over a year ago

Your research shows that includes is best.

Community · Accepted Answer · 2020-06-20 09:12:55Z

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 & 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 "specific" object consider:

JavaScript: alert({}!={}); alert({}!=={});

And thus:

JavaScript:

 obj = {prop:"value"}; 
 ra1 = [obj]; 
 ra2 = [{prop:"value"}];
 alert(ra1[0] == obj); 
 alert(ra2[0] == obj);

Often ra2 is considered to "contain" obj as the literal entity {prop:"value"}.

A very coarse, rudimentary, naive (as in code needs qualification enhancing) solution:

JavaScript:

  obj={prop:"value"};   ra2=[{prop:"value"}];
  alert(
    ra2 . toSource() . indexOf( obj.toSource().match(/^.(.*).$/)[1] ) != -1 ?
      'found' :
      'missing' );

See ref: Searching for objects in JavaScript arrays.

Eric Leschinski · Accepted Answer · 2019-01-30 14:48:00Z

-9

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.

edited Jan 30, 2019 at 14:48

Eric Leschinski

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answered Aug 4, 2010 at 14:05

Dennis Allen

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4 Comments

Tyler Over a year ago

But be careful: stackoverflow.com/questions/237104/javascript-array-containsobj/…

Yi Jiang Over a year ago

Please don't use a for in loop to iterate over an array - for in loops should be used strictly for objects only.

da coconut Over a year ago

why is it so bad

nkitku Over a year ago

please don't override builtins developers.google.com/web/updates/2018/03/smooshgate

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