Get the parameter contained in the page Url.

Call the function passing the parameter name as: getUrlParameter(“UserName“)

// strip parameters from URL
function getUrlParameter(sParam) {
var sPageURL = window.location.search.substring(1);
var sURLVariables = sPageURL.split('&');
 for (var i = 0; i < sURLVariables.length; i++) {
    var sParameterName = sURLVariables[i].split('=');
    if (sParameterName[0] == sParam) {
    return sParameterName[1];
    }
  }
};