function getParameterByName(){

   var locatStr = '?xyz=123&transaction[XXXX][zzzzz]=YYYYY',

       searchStr = locatStr.split('?')[1],

       matchArr = searchStr.match(/transaction\[[a-zA-Z0-9]+\]\[[a-zA-Z0-9]+\]/gi),       

       para;

  if(matchArr){

          var temp = searchStr.split(matchArr[0]+'=')[1];

        return ((temp.indexOf('&')!=-1) ? temp.split('&')[0] : temp);

      }

      else{

        return false;

      }

}

​

var param = getParameterByName();

console.log(param);

if(param){

  console.log('set cookie here');

}

else{

  console.log('no cookie present');

}

​