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

ECMAScript 6 introduced String.prototype.includes:

const string = "Hello World!";
const substring = "World";

console.log(string.includes(substring)); // true

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

var string = "Hello World!";
var substring = "Hello";

console.log(string.indexOf(substring) !== -1); // true

includes and indexOf performs a case-sensitive search