ES6 String contains, starts with, ends with to ES5

gistfile1.js

String.prototype.contains = String.prototype.contains || function(str) {
	return this.indexOf(str) >= 0;
};

String.prototype.startsWith = String.prototype.startsWith || function(prefix) {
	return this.indexOf(prefix) === 0;
};

String.prototype.endsWith = String.prototype.endsWith || function(suffix) {
	return this.indexOf(suffix, this.length - suffix.length) >= 0;
};