Edit in JSFiddle

function getUrlVars(param=null)
{
	if(param !== null)
	{
		var vars = [], hash;
		var hashes = window.location.href.slice(window.location.href.indexOf('?') + 1).split('&');
		for(var i = 0; i < hashes.length; i++)
		{
			hash = hashes[i].split('=');
			vars.push(hash[0]);
			vars[hash[0]] = hash[1];
		}
		return vars[param];
	} 
	else 
	{
		return null;
	}
}

/*
*
* URL :: http://example-domain.com?firstname=kang&lastname=cahya
*
* USAGE :: getUrlVars('firstname')
* RESULT :: kang
*
* USAGE :: getUrlVars('lastname')
* RESULT :: cahya
*
*/