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.

searchString

A string to be searched for within str.

position Optional

The position within the string at which to begin searching for searchString. (Defaults to 0.)

true if the search string is found anywhere within the given string; otherwise, false if not.

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

This method has been added to the ECMAScript 2015 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 (search instanceof RegExp) {
      throw TypeError('first argument must not be a RegExp');
    }
    if (start === undefined) { start = 0; }
    return this.indexOf(search, start) !== -1;
  };
}

• Polyfill of String.prototype.includes in core-js
• Array.prototype.includes()
• TypedArray.prototype.includes()
• String.prototype.indexOf()
• String.prototype.lastIndexOf()
• String.prototype.startsWith()
• String.prototype.endsWith()