var url = "https://myApp-ajj.com/sp?id=cat_item&sys_id=cf9f149cdbd25f00d080591e5e961920&sys_id1=cf9f149cdbd25f00d080591e5e961920&sysp_Id=a691acd9dbdf1bc0e9619fb&sysparm_CloneTable=sc_request&sysparm_CloneTable=sc_request"
url = url.slice(0, url.indexOf('&', url.indexOf('&') + 1));
console.log(url);
Попробуйте это :)