Why is jqXHR.responseText returning a string instead of a JSON object?

Question

I have an $.ajax() request with the dataType set to "json." The server is returning JSON with the correct mime type of "application/json." And yet the responseText in my jqXHR object is always a string. What am I doing wrong? Is this how it's supposed to work?

Here's how I'm making the call:

var options = { 
    dataType:'json',
    type: 'GET',
    url: "http://example.com/api/"
};

var key = "PassToCallback";

var jqXHRObject =  $.ajax(options).then(
    function(data, textStatus, jqXHR, key) {
        this.success(data, textStatus, jqXHR, key);
    },
    function(jqXHR, textStatus, errorThrown) { 
        this.error(jqXHR, textStatus, errorThrown);
    }
);

console.log(jqXHRObject.getResponseHeader("content-type")); // application/json
console.log(typeof jqXHRObject.responseText); // string

So I have have to do a $.parseJSON(jqXHRObject.responseText) to get an actual object. This seems unnecessary as $.ajax() should be automatically converting responseText according to the docs. Thanks!

Answer 1

I had the same problem. I returns a string because it formulated from an exception. E.g. I use a kernel listener with serialization to json on my Symfony2 project. Which is correct for proper REST headers.

Anyway, just parse it; this works for me:

$.ajaxSetup({
    "error": function(jqXHR, status, thrownError) {
        alert('error');
        var responseText = jQuery.parseJSON(jqXHR.responseText);
        console.log(responseText);
    }
});

Answer 2

Try

$.ajaxSetup({
    "error": function(jqXHR, status, thrownError) {
        alert('error');            
        console.log(jqXHR.responseJSON);
    }
});

Answer 3

You are using $.ajax in a way the docs don't describe. Using json as the dataType just means that the data passed to the success callback will be parsed. Use it like this:

$.ajax({
  dataType:'json',
  type: 'GET',
  url: "http://example.com/api/"
  success: function(data, textStatus, jqXHR) {
    // `data` contains parsed JSON
  },
  error: function(jqXHR, textStatus, errorThrown) {
     // Handle any errors
  }
});

Answer 4

I don't see anything in the documentation that suggests responseText would be anything other than exactly what the name implies: text.

Why not just use .getJSON? That would get rid of half of the code you wrote, and it'll convert the response to JSON. Win/win.

Answer 5

Step 1: Stringify the jqXHR

var errorString = JSON.stringify(jqXHR.responseText);

Step 2: change that string to Jquery Object

var $errorObj = $(errorString);

Step 3: Find and get what part of responseText you want.

var errorMessage = $errorObj.find('p').eq(1).text(); 

/* Here Im finding `Message:` thrown by the server, which is inside <p> tag */

Thats it.

$.ajax( /* ... */ ).fail( function(jqXHR, textStatus, errorThrown) {

     var errorString = JSON.stringify(jqXHR.responseText);
     var $errorObj = $(errorString);
     var errorMessage = $errorObj.find('p').eq(1).text();

     alert(errorMessage);

    } );