JavaScript equivalent of PHP's in_array()

Question

Is there a way in JavaScript to compare values from one array and see if it is in another array?

Similar to PHP's in_array function?

Alcot

FIRST SEE THIS ANSWER: #784512 tldr; var a = [1, 2, 3]; a.includes(2); // true – Kanzu

Answer 1

No, it doesn't have one. For this reason most popular libraries come with one in their utility packages. Check out jQuery's inArray and Prototype's Array.indexOf for examples.

jQuery's implementation of it is as simple as you might expect:

function inArray(needle, haystack) {
    var length = haystack.length;
    for(var i = 0; i < length; i++) {
        if(haystack[i] == needle) return true;
    }
    return false;
}

If you are dealing with a sane amount of array elements the above will do the trick nicely.

EDIT: Whoops. I didn't even notice you wanted to see if an array was inside another. According to the PHP documentation this is the expected behavior of PHP's in_array:

$a = array(array('p', 'h'), array('p', 'r'), 'o');

if (in_array(array('p', 'h'), $a)) {
    echo "'ph' was found\n";
}

if (in_array(array('f', 'i'), $a)) {
    echo "'fi' was found\n";
}

if (in_array('o', $a)) {
    echo "'o' was found\n";
}

// Output:
//  'ph' was found
//  'o' was found

The code posted by Chris and Alex does not follow this behavior. Alex's is the official version of Prototype's indexOf, and Chris's is more like PHP's array_intersect. This does what you want:

function arrayCompare(a1, a2) {
    if (a1.length != a2.length) return false;
    var length = a2.length;
    for (var i = 0; i < length; i++) {
        if (a1[i] !== a2[i]) return false;
    }
    return true;
}

function inArray(needle, haystack) {
    var length = haystack.length;
    for(var i = 0; i < length; i++) {
        if(typeof haystack[i] == 'object') {
            if(arrayCompare(haystack[i], needle)) return true;
        } else {
            if(haystack[i] == needle) return true;
        }
    }
    return false;
}

And this my test of the above on it:

var a = [['p','h'],['p','r'],'o'];
if(inArray(['p','h'], a)) {
    alert('ph was found');
}
if(inArray(['f','i'], a)) {
    alert('fi was found');
}
if(inArray('o', a)) {
    alert('o was found');
}  
// Results:
//   alerts 'ph' was found
//   alerts 'o' was found

Note that I intentionally did not extend the Array prototype as it is generally a bad idea to do so.

Poddy

jQuery.inArray() does not return boolean. It returns the index of the found element or -1 if not found – Ducat

Due to the high rating - you should mark your answer as outdated – Coston

this is documentation of indexOf w3schools.com/jsref/jsref_indexof_array.asp – Interlocutress

yes, this answer is outdated, the correct answers are below – Meemeece

Answer 2

There is now Array.prototype.includes:

The includes() method determines whether an array includes a certain element, returning true or false as appropriate.

var a = [1, 2, 3];
a.includes(2); // true 
a.includes(4); // false

Syntax

arr.includes(searchElement)
arr.includes(searchElement, fromIndex)

Reprography

Reminder: This doesn't work in IE11 (or any other version of Internet Explorer). For the rare cases were that still needs to be supported. – Ramirez

In the MDN function page there is a polyfill, but only in portuguese version: developer.mozilla.org/pt-BR/docs/Web/JavaScript/Reference/… – Shoreward

Answer 3

Array.indexOf was introduced in JavaScript 1.6, but it is not supported in older browsers. Thankfully the chaps over at Mozilla have done all the hard work for you, and provided you with this for compatibility:

if (!Array.prototype.indexOf)
{
  Array.prototype.indexOf = function(elt /*, from*/)
  {
    var len = this.length >>> 0;

    var from = Number(arguments[1]) || 0;
    from = (from < 0)
         ? Math.ceil(from)
         : Math.floor(from);
    if (from < 0)
      from += len;

    for (; from < len; from++)
    {
      if (from in this &&
          this[from] === elt)
        return from;
    }
    return -1;
  };
}

There are even some handy usage snippets for your scripting pleasure.

Manducate

This is a nicer/safer/better implementation of the links/code posted here already; the specs don't call for checking for arrays inside the haystack, and that's what the OP wants. – Poddy

Incidentally, what's the purpose of this.length >>> 0? Is that a conversion to a Number type? – Volcanology

Array.indexOf is now standardised by ECMAScript Fifth Edition so should be considered the proper ‘native’ way of doing it. You will still need to sniff and provide this backup for older browser for a long time, though. @harto: yes, it converts this.length to a Number that can be represented as a 32-bit unsigned integer. A native Array can only have a length that already complies with this, but the spec states that you can call Array.prototype methods on native-JS objects that are not Array. This and the other pedantic argument checking stuff is to guarantee absolute spec-compliance. – Saying

There's a different polyfill version available directly from Mozilla - developer.mozilla.org/en/docs/Web/JavaScript/Reference/… – Cece

@Volcanology I answer 8 years after your comment but maybe someone else could have the same question => see #1822850 – Quartile

Answer 4

PHP way:

if (in_array('a', ['a', 'b', 'c'])) {
   // do something if true
}

My solution in JS:

if (['a', 'b', 'c'].includes('a')) {
   // do something if true
}

Actuary

Answer 5

You can simply use the "includes" function as explained in this lesson on w3schools

it looks like

let myArray = ['Kevin', 'Bob', 'Stuart'];
if( myArray.includes('Kevin'))
console.log('Kevin is here');

Simpatico

Answer 6

If the indexes are not in sequence, or if the indexes are not consecutive, the code in the other solutions listed here will break. A solution that would work somewhat better might be:

function in_array(needle, haystack) {
    for(var i in haystack) {
        if(haystack[i] == needle) return true;
    }
    return false;
}

And, as a bonus, here's the equivalent to PHP's array_search (for finding the key of the element in the array:

function array_search(needle, haystack) {
    for(var i in haystack) {
        if(haystack[i] == needle) return i;
    }
    return false;
}

Cavazos

Nice drop in replacement. Really made porting from php to node easy. thanks – Selfrestraint

Answer 7

There is a project called Locutus, it implements PHP functions in Javascript and in_array() is included, you can use it exactly as you use in PHP.

Examples of use:

in_array('van', myArray);

in_array(1, otherArray, true); // Forcing strict type

Blind

There is also a inArray function in JQuery's APIs. Check api.jquery.com/jQuery.inArray – Amery

@ahPo, Nice! But the Locutus implementation has the advantage to be pure javascript with no dependencies. So, choose the best one for your needs – Blind

or you can just import the required function from Locutus. – Banlieue

Answer 8

jQuery solution is available, check the ducumentation here: http://api.jquery.com/jquery.inarray/

$.inArray( 10, [ 8, 9, 10, 11 ] );

Endosperm

don't forget to check like this: if($.inArray( 10, [ 8, 9, 10, 11 ] ) > -1) because I did like this: if($.inArray( 10, [ 8, 9, 10, 11 ] )) and it always returns true – Auspicate

PS: This is type sensitive so if checking for numbers make sure your datatypes match! ie: $.inArray( '10', [ 8, 9, 10, 11 ] ); would return -1 – Neutrality

Answer 9

var a = [1,2,3,4,5,6,7,8,9];

var isSixInArray = a.filter(function(item){return item==6}).length ? true : false;

var isSixInArray = a.indexOf(6)>=0;

Dual

Answer 10

There is an equivalent function:

includes()

Look here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/includes

Tempo

be carefull with that function it has currently no full browser support – Diffractometer

Answer 11

If you only want to check if a single value is in an array, then Paolo's code will do the job. If you want to check which values are common to both arrays, then you'll want something like this (using Paolo's inArray function):

function arrayIntersect(a, b) {
    var intersection = [];

    for(var i = 0; i < a.length; i++) {
        if(inArray(b, a[i]))
            intersection.push(a[i]);
    }

    return intersection;
}

This wil return an array of values that are in both a and b. (Mathematically, this is an intersection of the two arrays.)

EDIT: See Paolo's Edited Code for the solution to your problem. :)

Latoshalatouche

Although this is nice, it is not really what the OP asked for; it doesn't replicate the functionality of PHP's in_array. – Poddy

Answer 12

If you need all the PHP available parameters, use this:

function in_array(needle, haystack, argStrict) {
    var key = '', strict = !!argStrict;
    if (strict) {
        for (key in haystack) {
            if (haystack[key] === needle) {
                return true;
            }
        }
    }
    else {
        for (key in haystack) {
            if (haystack[key] == needle) {
                return true;
            }
        }
    }
    return false;
}

Hellbox

Answer 13

function in_array(needle, haystack){

    return haystack.indexOf(needle) !== -1;
}

Chaperon

This only returns whether it's the first element in the array; if indexOf(needle) > 0 it will return false – Vice

Answer 14

Add this code to you project and use the object-style inArray methods

if (!Array.prototype.inArray) {
    Array.prototype.inArray = function(element) {
        return this.indexOf(element) > -1;
    };
} 
//How it work
var array = ["one", "two", "three"];
//Return true
array.inArray("one");

Silicosis

Answer 15

With Dojo Toolkit, you would use dojo.indexOf(). See dojo.indexOf for the documentation, and Arrays Made Easy by Bryan Forbes for some examples.

Portal

Answer 16

haystack.find(value => value == needle)

where haystack is an array and needle is an element in array. If element not found will be returned undefined else the same element.

Highkey

Answer 17

function in_array(what, where) {
    var a=false;
    for (var i=0; i<where.length; i++) {
        if(what == where[i]) {
            a=true;
            break;
        }
    }
    return a;
}

Delighted

Answer 18

I found a great jQuery solution here on SO.

var success = $.grep(array_a, function(v,i) {
    return $.inArray(v, array_b) !== -1;
}).length === array_a.length;

I wish someone would post an example of how to do this in underscore.

Principe

Answer 19

An equivalent of in_array with underscore is _.indexOf

Examples:

_.indexOf([3, 5, 8], 8); // returns 2, the index of 8 _.indexOf([3, 5, 8], 10); // returns -1, not found

Clang

Answer 20

If you are going to use it in a class, and if you prefer it to be functional (and work in all browsers):

inArray: function(needle, haystack)
{
    var result = false;

    for (var i in haystack) {
        if (haystack[i] === needle) {
            result = true;
            break;
        }
    }

    return result;
}

Hope it helps someone :-)

Sincerity

Answer 21

var value = 'a';
var array = ['a', 'b', 'c'];
if(array.indexOf(value)){
    // exists in array
} else {
   // Not exists in array
}

Megalith

index of returns a number (not a boolean). if the value isn't present in the array -1 is returned – Udder