How to check if a string contains a substring in JavaScript

Created Apr 2, 2022 at 22:50

Modified Apr 2, 2022 at 23:01

Using String.prototype.includes

The includes() method performs a case-sensitive search to determine whether one string may be found within another string, returning true or false as appropriate.

'Google Docs will start'.includes('Docs'); // => true

// includes return true for empty substring
'Google Docs will start'.includes(''); // => true

// case-sensitive
'Google Docs will start'.includes('docs'); // => false

String.prototype.indexOf

includes doesn’t have Internet Explorer support, though. In ECMAScript 5 or older environments, use String.prototype.indexOf, which returns -1 when a substring cannot be found.

'Google Docs will start'.indexOf('Docs') !== -1; // => true

// an empty string is a substring of every string
'Google Docs will start'.indexOf('') !== -1; // => true

// case-sensitive
'Google Docs will start'.indexOf('Docs') !== -1; // => false

Polyfill

if (!String.prototype.includes) {
  String.prototype.includes = function(search, start) {
    'use strict';

    if (search instanceof RegExp) {
      throw TypeError('first argument must not be a RegExp');
    }
    if (start === undefined) { start = 0; }
    return this.indexOf(search, start) !== -1;
  };
}