javascript – Check if an element is present in an array

The Question :

618 people think this question is useful

The function I am using now to check this is the following:

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



It works. What I’m looking for is whether there is a better way of doing this.

The Question Comments :
• Looks fine to me. Of course, if your array is sorted you could do a binary-search instead. Or if each value in the array is always unique you could use a map-based approach instead.
• The == operator? Do you really want to explicitly allow type coercion? Of course not. Therefore, use the === operator instead.
• It’s smart to declare count before the loop. You could also replace those two lines with just for(var i=haystack.length; i--;)
• For numbers one can also use the in operator (e.g. (5 in array). It will probably be faster than other options, but won’t work for string or objects or any other non-number.

The Answer 1

1080 people think this answer is useful

ECMAScript 2016 incorporates an includes() method for arrays that specifically solves the problem, and so is now the preferred method.

[1, 2, 3].includes(2);     // true
[1, 2, 3].includes(4);     // false
[1, 2, 3].includes(1, 2);  // false (second parameter is the index position in this array at which to begin searching)



As of JULY 2018, this has been implemented in almost all major browsers, if you need to support IE a polyfill is available.

Edit: Note that this returns false if the item in the array is an object. This is because similar objects are two different objects in JavaScript.

The Answer 2

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Code:

function isInArray(value, array) {
return array.indexOf(value) > -1;
}



Execution:

isInArray(1, [1,2,3]); // true



Update (2017):

In modern browsers which follow the ECMAScript 2016 (ES7) standard, you can use the function Array.prototype.includes, which makes it way more easier to check if an item is present in an array:

const array = [1, 2, 3];
const value = 1;
const isInArray = array.includes(value);
console.log(isInArray); // true


The Answer 3

90 people think this answer is useful

Just use indexOf:

haystack.indexOf(needle) >= 0



If you want to support old Internet Explorers (< IE9), you’ll have to include your current code as a workaround though.

Unless your list is sorted, you need to compare every value to the needle. Therefore, both your solution and indexOf will have to execute n/2 comparisons on average. However, since indexOf is a built-in method, it may use additional optimizations and will be slightly faster in practice. Note that unless your application searches in lists extremely often (say a 1000 times per second) or the lists are huge (say 100k entries), the speed difference will not matter.

The Answer 4

39 people think this answer is useful

I benchmarked it multiple times on Google Chrome 52, but feel free to copypaste it into any other browser’s console.

~ 1500 ms, includes (~ 2700 ms when I used the polyfill)

var array = [0,1,2,3,4,5,6,7,8,9];
var result = 0;

var start = new Date().getTime();
for(var i = 0; i < 10000000; i++)
{
if(array.includes("test") === true){ result++; }
}
console.log(new Date().getTime() - start);



~ 1050 ms, indexOf

var array = [0,1,2,3,4,5,6,7,8,9];
var result = 0;

var start = new Date().getTime();
for(var i = 0; i < 10000000; i++)
{
if(array.indexOf("test") > -1){ result++; }
}
console.log(new Date().getTime() - start);



~ 650 ms, custom function

function inArray(target, array)
{

/* Caching array.length doesn't increase the performance of the for loop on V8 (and probably on most of other major engines) */

for(var i = 0; i < array.length; i++)
{
if(array[i] === target)
{
return true;
}
}

return false;
}

var array = [0,1,2,3,4,5,6,7,8,9];
var result = 0;

var start = new Date().getTime();
for(var i = 0; i < 10000000; i++)
{
if(inArray("test", array) === true){ result++; }
}
console.log(new Date().getTime() - start);



The Answer 5

24 people think this answer is useful

Single line code.. will return true or false

!!(arr.indexOf("val")+1)



The Answer 6

19 people think this answer is useful

You can use indexOf But not working well in the last version of internet explorer. Code:

function isInArray(value, array) {
return array.indexOf(value) > -1;
}



Execution:

isInArray(1, [1,2,3]); // true



I suggest you use the following code:

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



The Answer 7

9 people think this answer is useful

You can use the _contains function from the underscore.js library to achieve this:

if (_.contains(haystack, needle)) {
console.log("Needle found.");
};



The Answer 8

8 people think this answer is useful

Since ECMAScript6, one can use Set :

var myArray = ['A', 'B', 'C'];
var mySet = new Set(myArray);
var hasB = mySet.has('B'); // true
var hasZ = mySet.has('Z'); // false



The Answer 9

2 people think this answer is useful

In lodash you can use _.includes (which also aliases to _.contains)

You can search the whole array:

_.includes([1, 2, 3], 1); // true



You can search the array from a starting index:

_.includes([1, 2, 3], 1, 1);  // false (begins search at index 1)



Search a string:

_.includes('pebbles', 'eb');  // true (string contains eb)



Also works for checking simple arrays of objects:

_.includes({ 'user': 'fred', 'age': 40 }, 'fred');    // true
_.includes({ 'user': 'fred', 'age': false }, false);  // true



One thing to note about the last case is it works for primitives like strings, numbers and booleans but cannot search through arrays or objects

_.includes({ 'user': 'fred', 'age': {} }, {});   // false
_.includes({ 'user': [1,2,3], 'age': {} }, 3);   // false