Here you can find the source of startsWith(str)
String.prototype.startsWith = function(str) { return (this.match("^"+str)==str); };
String.prototype.startsWith = function(str) { return (this.indexOf(str) == 0); };
String.prototype.startsWith = function (str){ return this.indexOf(str) == 0; };
String.prototype.startsWith = function(str) { return (this.match("^"+str)==str); String.prototype.endsWith = function(str) { return (this.match(str+"$")==str);
String.prototype.startsWith = function(str){ return (this.indexOf(str) === 0);
String.prototype.startsWith = String.prototype.startsWith || function(str){ return this.substr(0,str.length) === str }; String.prototype.contains = String.prototype.contains || function(str){ return this.indexOf(str) >= 0 };
String.prototype.startsWith = function (str) { return this.indexOf(str) === 0; };
String.prototype.startsWith = function(str){ return this.slice(0, str.length) == str
String.prototype.startsWith = function(str) { if (typeof str !== 'string') return false; return this.indexOf(str) === 0; };
String.prototype.startsWith = function (str) { "use strict"; return (this.match("^" + str) == str); };