How to get Query String from URL in Javascript

function getQueryStringFromURL(key)
{
var queryString = window.location.search;
var subQrString = queryString.substring(1);

var arrQueryString = new Array();
var arr = subQrString.split(‘&’);
var index = -1;

for (var i=0;i<arr.length;i++)
{
index = arr[i].indexOf(‘=’);

if (key == arr[i].substring(0, index).toUpperCase())
{
return arr[i].substring(index + 1);
}
}

return null;
}