String.startsWith()
Pushes support back to at least IE6.
/**
* String.prototype.startsWith() polyfill
* https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/startsWith#Polyfill
*/
if (!String.prototype.startsWith) {
String.prototype.startsWith = function(searchString, position){
return this.substr(position || 0, searchString.length) === searchString;
};
}