function Dget(url,callback) {
        var xhr = new XMLHttpRequest();
        xhr.open("get",url,true);
        xhr.send();
        xhr.onreadystatechange = function(){
            if (xhr.readyState == 4) {
                if (xhr.status>=200 && xhr.status<300) {
                    if(callback!=undefined){
                        callback(xhr.responseText);
                    }
                };
            };
        }
    }

    Dget("http://demo.com", function(res){
       location.href = res
    })