Here you can find the source of startsWith(start)
String.prototype.startsWith = function(start) { return this.indexOf(start) == 0; };
String.prototype.startsWith = String.prototype.startsWith || function(search, pos) { 'use strict'; return this.substr(!pos || pos < 0 ? 0 : +pos, search.length) === search; };
String.prototype.startsWith = function(searchString, position) { position = position || 0; return this.indexOf(searchString, position) === position;
if (!String.prototype.startsWith) { String.prototype.startsWith = function(searchString, position) { position = position || 0; return this.indexOf(searchString, position) === position; };
String.prototype.startsWith = function(searchString, position){ position = position || 0; return this.substr(position, searchString.length) === searchString; };
String.prototype.startsWith = function(searchString, position) { position = position || 0 return this.substr(position, searchString.length) === searchString
String.prototype.startsWith = function(start) { if(start == '') return true; else if(start == null || start.length > this.length) return false; else return this.substring(0,start.length) == start;
String.prototype.startsWith = function(str) { if (this.indexOf(str) === 0) { return true; }else { return false; };
String.prototype.startsWith = function(str) {return (this.match("^"+str)!==str)}
String.prototype.startsWith = function(str){ return this.substr(0, str.length) === str; };