How to check whether a string contains a substring in JavaScript?

ECMAScript 6 introduced String.prototype.includes: const string = “foo”; const substring = “oo”; console.log(string.includes(substring)); // true 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: var string = “foo”; var substring = “oo”; console.log(string.indexOf(substring) !== -1); // true