从当前url替换获得新的url

function getUrlByReplaceThirdDomain(thirdDomain,pathName){
if(!thirdDomain || !pathName)
return;

if(pathName.indexOf('/')!=0){
pathName = '/' + pathName;
}
var domainArr=window.location.host.split('.');
var newDomain = domainArr.length>2 ? window.location.host.replace(domainArr[0],thirdDomain):window.location.host;
return window.location.protocol+'//'+newDomain+pathName;
}

console.log(getUrlByReplaceThirdDomain('user','abc/def'))