JavaScript URL parsing with regex - fallback for when window.URL isn't available

url.js

(function(URL, parent){

	var initialConstructor = parent.URL;

	var urlPattern = new RegExp(
		"^" +
			//protocol
			"(?:((?:\\w+):)?/?/?)" +
			//user:pass
			"(?:(?:([^:]*)(?::([^@]*))?)?@)?" +
			//host
			"(" +
				//hostname
				"([^:/?#]+)" +
				// port
				"(?:[:](\\d+))?" +
			")" +
			//pathname
			"([/][^?]*)?" +
			//search
			"([?][^#]*)?" +
			//hash
			"(#[^$]*)?" +
		"$", "i"
	);

	function URL(urlString, base){

		initialConstructor.apply(this, arguments);

		if(base instanceof URL){
			urlString = base.href + '/' + urlString;
		}else if(base){
			urlString = base + '/' + urlString;
		}

		urlString = urlString.trim();

		var urlMatch = urlString.match(urlPattern);

		if(!urlMatch){
			throw new TypeError('Failed to construct \'URL\': Invalid URL');
		}

		//replace matched undefined/null with ""
		for(var i = 0; i < urlMatch.length; i++){
			urlMatch[i] = urlMatch[i] == undefined ? "" : urlMatch[i];
		}

		this.hash = urlMatch[9];
		this.host = urlMatch[4];
		this.hostname = urlMatch[5];
		this.href = urlString;
		this.origin = urlMatch[1] + '//' + urlMatch[4];
		this.username = urlMatch[2];
		this.password = urlMatch[3];
		this.pathname = urlMatch[7];
		this.port = urlMatch[6];
		this.protocol = urlMatch[1];
		this.search = urlMatch[8];
		
	}

	parent.URL = URL;

	URL.prototype = initialConstructor.prototype;

	URL.createObjectURL = function(){
		console.error('URL.createObjectURL() is not supported');
	}

	URL.revokeObjectURL = function(){
		console.error('URL.revokeObjectURL() is not supported');
	}

	URL.prototype.toString = function(){
		return this.href;
	}

})