How to callback a function on 404 in JSON ajax req

Question

I want to make an Ajax request with response in JSON. So I made this Ajax request:

$.ajax({
    url: 'http://my_url',
    dataType: "json",
    success: function(data){
      alert('success');
    },
    error: function(data){
      alert('error');
    },
    complete: function(data) {
      alert('complete')
    }})

This code works good but when my url send me a HTTP code 404, no callbacks are used, even the complete callback. After research, it's because my dataType is 'json' so 404 return is HTML and the JSON parsing failed. So no callback.

Have you a solution to call a callback function when a 404 is raised ?

EDIT: complete callback don't call is return is 404. If you want an URL wit 404 you can call : http://twitter.com/status/user_timeline/jksqdlmjmsd.json?count=3&callback=jsonp1269278524295&_=1269278536697 it's with this URL I have my problem.

Answer 1

Is it simply because the dataType is set to "json"? If so, try changing it to text and evaluate the JSON yourself:

$.ajax({
    url: 'http://twitter.com/status/user_timeline/jksqdlmjmsd.json?count=3&callback=jsonp1269278524295&_=1269278536697',
    dataType: 'text',
    success: function(data, status, xmlHttp) {
        try {
            data = eval('(' + data + ')');
            alert('success');
        } catch (e) {
            alert('json parse error');
        }
    },
    error: function(xmlHttp, status, error) {
        alert('error');
    },
    complete: function(xmlHttp, status) {
        alert('complete');
    }
});

Answer 2

With your configuration jQuery uses jsonp to transport the data. This works by dynamically inserting a script element and setting the URL to the specified value. The data returned by the server is then evaluated as JavaScript - usually calling the provided callback. If the server returns a 404, the contents is obviously no JavaScript and the callback is never called. Some browsers support error handlers on the script tag, which are called in these situations. Unfortunately IE doens't support this. The best way to detect an error is to rely on a timeout.

In your case you should specify an additional timeout option, which causes the error handler to be called if the callback wasn't called in time (which would be the case for a 404 response).

$.ajax({
  url: 'http://my_url',
  timeout: 2000, // 2 seconds timeout
  dataType: "json",
  success: function(data){
    alert('success');
  },
  error: function(data){
    alert('error');
  },
  complete: function(data) {
    alert('complete')
  }
});

Answer 3

Are you aware that even though the HTTP status is 404, the actual body is valid JSON? For instance, this link has the following JSON:

jsonp1269278524295({"request":"/status/user_timeline/jksqdlmjmsd.json?count=3&callback=jsonp1269278524295&_=1269278536697","error":"Not found"})

As such, you should check if your data has the error property within your normal callback function.

UPDATE: apparently, even though the actual content of the page is valid JSON, the browser (I checked in Firefox) is not executing it, most likely because it is a 404. Because jQuery has to add a script element (because of the cross-domain issue), its JSONP wrapper is never called, and as a consequence, neither are your callbacks.

So, in short, I don't think there is a way to deal with this without manually adding that script element and checking if your pre-defined callback function has been called afterwards.

Answer 4

Use the statusCode-Option

$.ajax({
    url: 'http://my_url',
    dataType: "json",
    statusCode: {
        404: function() {
            alert("I could not find the information you requested.");
        }
    },
    success: function(data) {
      alert('success');
    },
    error: function(data) {
      alert('error');
    },
    complete: function(data) {
      alert('complete');
    }
})