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18

1407

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"));

Overpraise answered 25/7, 2009 at 8:18 Comment(12)

The code works in Safari 4.0.2. BTW: I'd do a === comparison instead of just ==. – Jorrie 25/7, 2009 at 8:45

"The above function always returns false." No it doesn't: The function works as expected - the error must be somewhere else. – Nodus 25/7, 2009 at 8:59

See also: https://mcmap.net/q/36072/-how-do-i-check-if-an-array-includes-a-value-in-javascript/1569 – Adele 18/2, 2011 at 21:8

Finally its worked. its due to improper trim of the comparing value. there was some space in the comparing value (A comment from the asker, to the accepted answer.) – Pasta 1/10, 2012 at 9:9

It works, you should have used === instead of == – Columbic 11/4, 2016 at 15:40

For whoever is still struggling with it. The following took care of it for me: 1. Install lodash.includes by executing the following command: npm --save lodash.includes 2. Require lodash.includes: var includes = require('lodash.includes'); 3. use it like this: arrayBeingUsed.includes(valueToLookFor); (npmjs.com/package/lodash.includes) – Extrude 22/11, 2016 at 19:48

Related with better answer - https://mcmap.net/q/46286/-check-if-an-element-is-present-in-an-array-duplicate – Anecdotist 5/1, 2017 at 16:4

["Admin", "Action", "WriteType"].find( (key) => { console.log(key = , key); return key === "KeyWord" } ); – Scotney 25/8, 2017 at 7:0

developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… – Scotney 25/8, 2017 at 7:1

you can use Lodash _.some(arrValues,'Sam') => true /false – Sextain 21/3, 2018 at 19:11

if(numbers.join('') == '') then it means array named 'numbers' is empty. – Plowshare 17/6, 2019 at 16:58

there is no contains method in javascript for array, you can use includes instead – Tapdance 17/10, 2020 at 5:45

F

1013

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 && typeof Array.prototype.indexOf === 'function') {
        indexOf = Array.prototype.indexOf;
    } else {
        indexOf = function(needle) {
            var i = -1, index = -1;

            for(i = 0; i < this.length; i++) {
                var item = this[i];

                if((findNaN && item !== item) || item === needle) {
                    index = i;
                    break;
                }
            }

            return index;
        };
    }

    return indexOf.call(this, needle) > -1;
};

You can use it like this:

var myArray = [0,1,2],
    needle = 1,
    index = contains.call(myArray, needle); // true

CodePen validation/usage

Facet answered 25/7, 2009 at 8:22 Comment(24)

Note that indexOf on arrays is not implemented in IE, but you can define it yourself – Courtund 25/7, 2009 at 8:36

you should use a typed comparison with === to be compatible with the native implementation – Nodus 25/7, 2009 at 9:8

fixed the comparison and added the missing return -1; please note that according to the ES5 spec, this method will behave differently from the native one in case ofsigned zeroes and NaNs (see 15.4.4.14 and 9.12 vs. 11.9.6) – Nodus 25/7, 2009 at 9:26

I have tried all the answers given , but still returning false. – Overpraise 25/7, 2009 at 10:52

Finally its worked. its due to improper trim of the comparing value. there was some space in the comparing value – Overpraise 25/7, 2009 at 11:10

What version of IE does this answer refer to? – Andrews 24/2, 2012 at 22:20

The shim should test if i is a property of this. – Biernat 5/3, 2013 at 19:12

Note that in Sharepoint 2010, WebParts can break if you implement an Array.Prototype: labs.steveottenad.com/type-mismatch-on-wpadder-js – Ambur 2/4, 2013 at 15:21

@thesystem, that's an odd concern for a method of Array.prototype and an i that is numeric and bound by 0 and this.length. I think we can safely assume that i is a property of this, given those characteristics. I suppose it could be an issue if you call Array.prototype.indexOf.call(someArbitraryObjectWithALengthProperty), but that would be true of the native method as well. – Facet 23/6, 2013 at 7:43

@wilsjd, I have been meaning to update this for some time, to warn against patching prototypes. – Facet 23/6, 2013 at 7:44

var i = -1, index; Can anyone explain this part? (it returns undefined if the needle is not found in the array) testing on IE8, works fine for firefox – Sorrells 6/8, 2013 at 12:17

How about this: ~array.indexOf(value) -- It'll be truthy if the value exists and falsy otherwhise. So you could do something like: if (~array.indexOf(value)) { console.log('Found it!'); } – Caterinacatering 24/7, 2014 at 17:18

@gtramontina, that is very "clever" but confusing to anyone who doesn't know what it does. In order to make it maintainable, you'd overcome your savings in code characters by documenting it with a comment. – Facet 24/7, 2014 at 20:32

@Facet I'd rather document it with tests. – Caterinacatering 24/7, 2014 at 22:29

@gtramontina, but if anyone else has to read your code, it will be confusing. If not, do whatever you want... but then that calls into question advocating it on a Q&A site. – Facet 25/7, 2014 at 1:19

@Caterinacatering Why would you do a bitwise not (~) rather than a logical not (!)? I guess in this case the end result is the same, but as the next person reading your code, I would spend a few minutes puzzling on that one, as I just did. – Degrade 21/11, 2014 at 14:41

A logical not (!) on its own – i.e. if (!array.indexOf(value)) – would fail the case where the element exists on the first position (0), as 0 is falsy. – Caterinacatering 26/11, 2014 at 0:32

Doesn't work for NaN – Il 5/1, 2016 at 0:14

@threed, that's a good catch, but I'm a little stumped about how best to fix it for SO users. I briefly edited the non-native implementation to handle NaN, then checked it in CodePen; I realized that the native Array.prototype.indexOf method (at least in Chrome) also doesn't support NaN. So on the one hand, the behavior is technically incorrect, but on the other hand it has parity with what the browser provides. I know how I'd solve it in my own projects (a wrapper function, completely sidestepping the native implementation for NaN), but I'm cautious about misdirecting SO users. – Facet 5/1, 2016 at 2:39

@threed, thinking more on this, I realize the actual question is not about indexOf, that was just an implementation detail. I'll more thoroughly update the answer. – Facet 5/1, 2016 at 2:40

Good call. I recommend taking a look at the MDN polyfill for the Array.includes method. – Il 5/1, 2016 at 2:42

@threed, I took a look at the MDN page, and I honestly found it hard to read. That said, I've updated my answer to handle NaN (and included the CodePen) – Facet 5/1, 2016 at 2:50

var numbers = [0,1,2,3,4,5,6,7,8,9]; return jQuery.inArray( parseInt(e.key), numbers )!=-1; – Trotman 27/12, 2016 at 7:38

[1, 2, 3].includes(2); Array.includes(val) is available since year 2016 – Admire 21/2, 2017 at 15:26

V

1021

jQuery has a utility function for this:

$.inArray(value, array)

Returns index of value in array. Returns -1 if array does not contain value.

Vd answered 24/9, 2009 at 19:34 Comment(9)

Don't let the name "inArray" fool you. As mentioned above (but of course I didn't read closely enough), returns -1 (not false) if the element doesn't exist. – Meso 19/4, 2011 at 20:13

@Steve Paul what is wrong with name? it does what it says: -1=it's NOT there, anything else= it's there – Cherlynchernow 22/6, 2013 at 18:9

'inArray' implies that a boolean will be returned indicating whether the element could be found in the array. Therefore users may feel tempted to use the expression: if ($.inArray('myval', myarray)) {...} This will evaluate to true if 'myval' is NOT in myarray. Furthermore, it will evaluate to false if myval's index is 0. – Gobi 24/6, 2013 at 5:11

The non-booleanness of $.inArray's return definitely feels like a mistake on jQuery's part. Surely, it ought to be renamed to $.indexOf, if that's the function it's polyfilling? – Nightclub 7/3, 2014 at 23:1

Works, but requires the jQuery framework. Not ideal if you're not using it otherwise. – Menology 30/12, 2014 at 2:10

It's very easy to suggest that someone uses a JQuery method for everything javascript, but as the original question was for a javascript solution, then one should be provided in that manner – Impromptu 1/10, 2015 at 12:40

Does not work for NaN – Il 5/1, 2016 at 0:16

Also worth mentioning that $.inArray('0', ['0', '1', '2']) will return 0, which should be true, but inside and if it evaluates to false. – Infantry 23/1, 2017 at 18:23

You could use a bitwise operator like if (!~$.inArray(0, [13, 27, 35, 36, 37, 38, 39, 40])) {}. The tilde (~) transforms -1 to 0 and 0 is equal to false in Javascript. – Dorothadorothea 21/6, 2018 at 12:34

F

1013

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 && typeof Array.prototype.indexOf === 'function') {
        indexOf = Array.prototype.indexOf;
    } else {
        indexOf = function(needle) {
            var i = -1, index = -1;

            for(i = 0; i < this.length; i++) {
                var item = this[i];

                if((findNaN && item !== item) || item === needle) {
                    index = i;
                    break;
                }
            }

            return index;
        };
    }

    return indexOf.call(this, needle) > -1;
};

You can use it like this:

var myArray = [0,1,2],
    needle = 1,
    index = contains.call(myArray, needle); // true