find-if-an-item-is-in-a-javascript-array

http://stackoverflow.com/questions/143847/best-way-to-find-if-an-item-is-in-a-javascript-array

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

 

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This question already has an answer here:

• How do I check if an array includes an object in JavaScript? 33 answers

What is the best way to find if an object is in an array?

This is the best way I know:

function include(arr, obj) {
    for(var i=0; i<arr.length; i++) {
        if (arr[i] == obj) return true;
    }
}
include([1,2,3,4], 3); // true
include([1,2,3,4], 6); // undefined

javascript arrays

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edited Jan 6 at 21:05 Gothdo 18.4k104879

asked Sep 27 '08 at 15:41 zimbatm 3,60041411

marked as duplicate by Gothdojavascript Jan 6 at 21:04

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

See: stackoverflow.com/a/25765186/1320932 – dr.dimitru Sep 10 '14 at 12:18

3

2 things: 1.) 'include' is a really bad name for a function that does not modify the state of anything. It's especially bad for a function that simply returns a boolean. 2.) You need to add "return(false);" before the end of the function. – Aquarelle May 12 '15 at 0:57 

as of ECMAScript 2016, you can use Array.prototype.includes function: myArray.includes(3); // true – mhdJun 15 '16 at 13:25 

1

In ES6 you can do something like arr.find(lamda function) , example: [1, 2, 3,4,5].find(x => x == 3). if element is found it is returned else undefined is returned – allsyed Jul 29 '16 at 10:26 

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8 Answers

activeoldestvotes

up vote565down voteaccepted

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:

1. Mozilla's (ECMA-262) version:

     if (!Array.prototype.indexOf)
     {
          Array.prototype.indexOf = function(searchElement /*, fromIndex */)
       {
       "use strict";
       if (this === void 0 || this === null)
         throw new TypeError();
       var t = Object(this);
       var len = t.length >>> 0;
       if (len === 0)
         return -1;
       var n = 0;
       if (arguments.length > 0)
       {
         n = Number(arguments[1]);
         if (n !== n)
           n = 0;
         else if (n !== 0 && n !== (1 / 0) && n !== -(1 / 0))
           n = (n > 0 || -1) * Math.floor(Math.abs(n));
       }
       if (n >= len)
         return -1;
       var k = n >= 0
             ? n
             : Math.max(len - Math.abs(n), 0);
       for (; k < len; k++)
       {
         if (k in t && t[k] === searchElement)
           return k;
       }
       return -1;
     };
   }

2. Daniel James's version:

   if (!Array.prototype.indexOf) {
     Array.prototype.indexOf = function (obj, fromIndex) {
       if (fromIndex == null) {
           fromIndex = 0;
       } else if (fromIndex < 0) {
           fromIndex = Math.max(0, this.length + fromIndex);
       }
       for (var i = fromIndex, j = this.length; i < j; i++) {
           if (this[i] === obj)
               return i;
       }
       return -1;
     };
   }

3. 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);
     }
   );

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edited Nov 29 '12 at 10:40

answered Sep 27 '08 at 15:45 Vinko Vrsalovic 172k36279330

I'm curious as to why your version of the Mozilla function is so different from the website you're linking to. Did you modify it yourself or is it just an old version or something? – Shenjoku Mar 11 '14 at 1:16

4

@Shenjoku: "answered Sep 27 '08 at 15:45" – Vinko Vrsalovic Mar 11 '14 at 5:49

Well, there's my answer haha. I can't tell if there's an older version just by looking at the mozilla website so I wasn't sure. Not that it matters, just a curiosity. In any case this was still helpful so you get an upvote ;) – Shenjoku Mar 13 '14 at 2:24

1

@mcktimo You actually can delete your own comments - if you mouse over your comment, you will see a small circle with an "X" inside; clicking this will prompt to confirm deletion. – Jesse Apr 18 '14 at 21:06

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up vote188down vote

If you are using jQuery:

$.inArray(5 + 5, [ "8", "9", "10", 10 + "" ]);

For more information: http://api.jquery.com/jQuery.inArray/

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edited Apr 23 '16 at 4:28 ozgur 18.1k82965

answered Mar 27 '10 at 0:37 GerManson 3,80711217

Note that "inArray" is a misnomer, because it doesn't return boolean value - it returns index of first element found. So if you are checking if element exists you should use if (-1 != $.inArray(...)) .... – johndodo 2 days ago

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up vote31down vote

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 < 0) {
            fromIndex = Math.max(0, this.length + fromIndex);
        }
        for (var i = fromIndex, j = this.length; i < 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 < 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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edited Jul 26 '12 at 15:21 Bill the Lizard 233k140455746

answered Sep 27 '08 at 18:10 Daniel James 3,3591328

The code examples you are linking to are slow on large arrays. See the comments in my implementation example of a hasItem() function. – roosteronacid Sep 27 '08 at 23:06

Take a look at these benchmarks: blogs.sun.com/greimer/resource/loop-test.htm For-loops are slow. But I guess the arrays used in the benchmarks are pretty huge :) – roosteronacid Sep 28 '08 at 11:28

1

blogs.sun.com/greimer/resource/loop-test.html – roosteronacid Sep 28 '08 at 11:37

I agree. I'm also quite pragmatic. But in the case of optimizing the very basics of the language, I think it's good design to implement functionality as performance-effective as possible. – roosteronacid Sep 28 '08 at 15:14

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up vote9down vote

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:

1. Pick the middle element of the array.
2. 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.
3. 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.

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edited Sep 27 '08 at 16:00

answered Sep 27 '08 at 15:50 assortedslog 1013

1

You probably should mention that this approach would be faster on large, sorted arrays than small ones. – roosteronacid Sep 27 '08 at 23:07

9

why would this be slower on smaller arrays? – vidstige Aug 22 '11 at 7:54

1

@vidstige: He means it scales well, but isn't necessarily fastest for small inputs. – Lightness Races in OrbitFeb 11 '14 at 12:53 

This runs in O(lg n) as opposed to O(n), which is way more scalable – Edmund Sep 22 '14 at 19:09

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up vote9down vote

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

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edited Apr 16 '16 at 15:34

answered Feb 24 '12 at 18:11 bortunac 1,4811212

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up vote3down vote

It depends on your purpose. If you program for the Web, avoid indexOf, it isn't supported by Internet Explorer 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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edited Aug 11 '11 at 23:55 Peter Mortensen 10.8k1375109

answered Sep 27 '08 at 16:28 PhiLho 30.7k262107

ha...I shrill to think there's still an IE6 client out there at this point... – beauXjames Aug 15 '14 at 16:25

shouldn't there be a "as of 2008" like in wikipedia page so that people know this statement is certainly outdated – allan.simon May 5 '16 at 14:20

2

@allan.simon Look at my icon (and stats) at the bottom of my answer. Just above, there is "answered Sep 27 '08 at 16:28". It is called a date, and people used to Stack Overflow look at these dates to take answers with a grain of salt... That said, my local public library still has IE6 installed on their computers! (but somebody installed Chrome, fortunately!) – PhiLho May 5 '16 at 22:36

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up vote3down vote

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
            && 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;
}

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edited Aug 22 '11 at 7:47

answered Aug 17 '11 at 12:57 Ariana Carter-Weir 1,094616

While this may theoretically answer the question, it would be preferable to include the essential parts of the answer here, and provide the link for reference. Also, when you copy/paste the same link-only answer to several very old questions at once, it just looks like spam. – Bill the Lizard Aug 18 '11 at 12:48 

Sorry Bill, I really didn't mean it to seem like spam and was just trying to update a few of the old questions about this topic too. I've edited the post here to include the actual answer instead of linking off. – Ariana Carter-Weir Aug 22 '11 at 7:37

@Bill, actually re-reading the question, this doesn't even answer it at all. I must have made a mistake. – Ariana Carter-Weir Aug 22 '11 at 7:40

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up vote3down vote

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

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edited Nov 2 '12 at 2:16 Dan Dascalescu 38k15144184

answered Sep 27 '08 at 15:51 Paul Dixon 194k35253303

2

Weird URL for a manual containing information about Javascript 1.8 and beyond! :) – Vinko Vrsalovic Sep 27 '08 at 15:56

this doesnt cover object arrays like the author asked about – 29er May 31 '12 at 6:12

@VinkoVrsalovic: the URL has changed to developer.mozilla.org/en-US/docs/JavaScript/Reference/… – Dan Dascalescu Nov 2 '12 at 2:14

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