String.prototype.includes()

Summary

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.

Description

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

Examples

Example: 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() {
    return String.prototype.indexOf.apply(this, arguments) !== -1;
  };
}

Specifications

Browser compatibility

String.prototype.contains

In Firefox 18 - 36, the name of this method was called "contains". It was renamed to "includes" in bug 1102219 due to the following reason:

It's been reported that some Web sites using MooTools 1.2 broke on Firefox 17. This version of MooTools checks whether String.prototype.contains() exists and, if it doesn't, adds its own. 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, this change was disabled in Firefox 17. String.prototype.contains() is available one version later, Firefox 18.

MooTools 1.3 forces its own version of String.prototype.contains(), so Web sites 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). MooTools 1.5+ changed the signature to match the ES6 standard.

See also

• String.prototype.indexOf()
• String.prototype.lastIndexOf()
• String.prototype.startsWith()
• String.prototype.endsWith()