Get QueryString Data using javascript

Assume the url is "http://localhost:portnumber/site/pages/page.aspx?Id=1

javascript function:

function getQueryProjectNum(variable)
{
var query = window.location.search.substring(1);
var vars = query.split("&");
for (var i=0;i<vars.length;i++)
{
var pair = vars[i].split("=");
if (pair[0] == variable)
{
return pair[1];
}
}
}

var Id= getQueryProjectNum("Id");