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up vote 2310 down vote favorite
417

What is the most concise and efficient way to find out if a JavaScript array contains an obj?

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.

share|improve this question
25  
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 Jul 2 '12 at 11:56
13  
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 Oct 2 '13 at 7:59
3  
~ 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 Jun 20 '14 at 12:49
    
IE9 supports indexOf() as per w3schools.com/jsref/jsref_indexof_array.asp. If older browser better approach is to define prototype for indexOf() function as given in Array.indexOf in Internet Explorer – Lijo Jan 21 '15 at 21:42
6  
@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 Mar 14 '15 at 5:35

32 Answers 32

1 2
up vote -3 down vote

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.

share|improve this answer
up vote -5 down vote

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;
}
share|improve this answer
1  
But be careful: stackoverflow.com/questions/237104/javascript-array-contains‌​obj/… – MatrixFrog Aug 12 '10 at 23:18
19  
Please don't use a for in loop to iterate over an array - for in loops should be used strictly for objects only. – Yi Jiang Jan 20 '11 at 16:33
1 2

protected by Josh Crozier Feb 14 '14 at 23:10

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