JavaScript is becoming more and more popular as a language for SharePoint solutions. Time to get familiar with the built-in JavaScript repository. I have seen quite of different ways to retrieve querystring parameter values in JavaScript, but SharePoint features it’s own function ‘_spGetQueryParam(p)’.

The function ‘_spGetQueryParam(p)’ is loaded from the ‘init.js’:

function _spGetQueryParam(p)
{ULSA13:;
	var q=window.location.search.substring(1);
	if(q && q.length > 2)
	{
		var params=q.split("&");
		var l=params.length;
		for (var i=0;i<l;i++)
		{
			var pair=params[i].split("=");
			if (pair[0].toLowerCase()==p)
				return pair[1];
		}
	}
}

You need to provide the lowercase name of the parameter to retrieve the value; e.g.:

var currentFolder = _spGetQueryParam('rootfolder')