关于Ajax的疑难杂症详解

     <?php
     header("Access-Control-Allow-Origin: *");

      function index(){
       sleep(2);
       return  JSON_encode(['code'=>8888888]);
      }

      echo index();
     ?>

<script>
  var data = {
    parent:1
  }
  $.ajax({
    type: "POST",
    url: "http://127.0.0.1",
    dataType:'json',
    success: function (response,index,obj) {

      console.log(obj.done(function() {  //延迟请求成功后的回调
      alert("$.get succeeded"); 
      }));  

      console.log(index);     //log success
      console.log("成功",response);   //请求成功返回的数据
    },
    error(res){
      console.log("失败",res);
    }
  });
</script>