JSFiddle - React, Tailwind, and code Playground

HTML

<div id="output"></div>

JavaScript

var querystring = "http://test.com/?xnJTqqWEclJnnPEvWH&cid=cHJvdmlzaW9uAElhbkJyZW5uYW5AMWU2ZDY2LnZpZHlvLmlvADY0ODc1NDY2NDYyAAAwZGU0N2MzYmM3OWQ1YjQzYzM5NDEzYWRmNGRlYmRkZDRiOGJhZjM5Yzg4MmIwZjVlN2NiMDM1ZDM0NmYzNTFmODhjNGZhMjQxMmU2ODBhNzQyNmE3MzJkNGRkZTAzOGE=&displayName=sfafdsf&mid=3D93-36-14-46-4D-52-9E-48-17-=6A-50-13-56-FA-0A-06&PROMO_MONTH=3D201106";

$("#output").html(gup('cid'));

function gup( name )
{
  name = name.replace(/[\[]/,"\\\[").replace(/[\]]/,"\\\]");
  var regexS = "[\\?&]"+name+"=([^&#]*)";
  var regex = new RegExp( regexS );
//  var results = regex.exec( window.location.href );
  var results = regex.exec(querystring);
  if( results == null )
    return "";
  else
  console.log(results)
    return results[1];
}