1-2 封装ajax

function ajax({
    url,
    method = "get",
    success
}){
   var xhr =  new XMLHttpRequest();
   xhr.open(method,url,true);
   xhr.send();
   xhr.onreadystatechange = function(){
       if(xhr.readyState == 4 && xhr.status == 200){
           var result = JSON.parse(xhr.responseText);
           success(result)
       }
   }
}