The includes() method determines whether one string may be found within another string, returning true or false as appropriate.


str.includes(searchString[, position])


A string to be searched for within this string.
Optional. The position in this string at which to begin searching for searchString; defaults to 0.

Return value

true if the string contains the search string; otherwise, false.


This method lets you determine whether or not a string includes another string.


The includes() method is case sensitive. For example, the following expression returns false:

'Blue Whale'.includes('blue'); // returns false


Using includes()

var str = 'To be, or not to be, that is the question.';

console.log(str.includes('To be'));       // true
console.log(str.includes('question'));    // true
console.log(str.includes('nonexistent')); // false
console.log(str.includes('To be', 1));    // false
console.log(str.includes('TO BE'));       // false


This method has been added to the ECMAScript 6 specification and may not be available in all JavaScript implementations yet. However, you can easily polyfill this method:

if (!String.prototype.includes) {
  String.prototype.includes = function(search, start) {
    'use strict';
    if (typeof start !== 'number') {
      start = 0;
    if (start + search.length > this.length) {
      return false;
    } else {
      return this.indexOf(search, start) !== -1;


Specification Status Comment
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'String.prototype.includes' in that specification.
Standard Initial definition.
ECMAScript 2017 Draft (ECMA-262)
The definition of 'String.prototype.includes' in that specification.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Edge Opera Safari
Basic support 41 40 (40) No support 14393+ No support 9
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support No support No support 40.0 (40) No support No support No support


In Firefox 18 - 39, the name of this method was contains(). It was renamed to includes() in bug 1102219 due to the following reason:

It's been reported that some websites using MooTools 1.2 broke on Firefox 17. This version of MooTools checks whether String.prototype.contains() exists and, if it doesn't,  MooTools adds its own function. With the introduction of this function in Firefox 17, the behavior of that check changed in a way that causes code based on MooTools' String.prototype.contains() implementation to break. As a result, the implementation was disabled in Firefox 17 and String.prototype.contains() was available one version later, in Firefox 18, when outreach to MooTools was leading to the release of MooTools version 1.2.6.

MooTools 1.3 forces its own version of String.prototype.contains(), so websites relying on it should not break. However, you should note that MooTools 1.3 signature and ECMAScript 6 signatures for this method differ (on the second argument). Later, MooTools 1.5+ changed the signature to match the ES6 standard.

In Firefox 48, String.prototype.contains() has been removed. Use String.prototype.includes() only.

See also

Document Tags and Contributors

 Last updated by: ex1st,