Why is my Jquery.ajax call triggering error event?

Question

When I call the following jquery.ajax it always returns a fail. When I look further into the response it shows an ok status and 200 response.

Why is it throwing a "fail" event?

 $.ajax({
    url: "myurl",
    type: "POST",
    contentType: "application/json; charset=utf-8",
    data: mydata,
    dataType: "json"
}).done(function (data) { 
      alert("success" + data.slice(0, 100)); })
  .fail(function (v) { 
      console.log(v); })
  .always(function (v) { 
      alert("complete"+v); 
});

The data is reaching my backend url correctly.

Answer 1

我确保服务器以一些有效的json数据响应并且一切正常。