Validate the existence of a substring in ES5 and older

The String.prototype.includes() method was introduced in the ES6 o ES2015, and performs a search to determine whether a given string may be found within this string, returning true or false as appropriate.

But we can achieve the same result in older versions of JS using the String.prototype.indexOf() method:

var myString = "Hello, World!";
var substring = "World";

if (myString.indexOf(substring) !== -1) {
    console.log("Substring found!");
    return true;
} else {
    console.log("Substring not found.");
    return false;
}