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The includes()
method determines whether one string may be found within another string, returning true
or false
as appropriate.
Syntax
str.includes(searchString[, position])
Parameters
searchString
- A string to be searched for within this string.
position
- 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
.
Description
This method lets you determine whether or not a string includes another string.
Case-sensitivity
The includes()
method is case sensitive. For example, the following expression returns false:
'Blue Whale'.includes('blue'); // returns false
Examples
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
Polyfill
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; } }; }
Specifications
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. |
Draft |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | 41 | 40 (40) | No support | 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 |
String.prototype.contains
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.