ajax原生写法
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
})