Can I force jQuery Deferred/Ajax to execute fail handler after it has been resolved?

Question

An example to make clear what i want to do. This is what I would usually do:

function success(data, status, jqxhr){
  if ( data.error )
    return failure(jqxhr, status, data.error);
  // process data
}
function failure(jqxhr, status, err){
  ...
}

$.ajax( ... )
  .done(success)
  .fail(failure)

Is there any way, i can accomplish this with anonymous functions only, like so?

   $.ajax( ... )
      .done(function(data, status, jqxhr){
         if(data.error)
            // what do i need to do here to jump in to the fail handler?
      })
      .fail(function(jqxhr, status, err){
         ...
      })

I know that. Is there still any way to force the execution of failure handlers? — lordvlad, Jan 14 '14 at 10:13
technically you can use a goto. But in practice it's better not to do it — Fabrizio Calderan, Jan 14 '14 at 10:13
@NabilKadimi, then i would need an additional check, whether always was called after a success or failure, but it's an idea — lordvlad, Jan 14 '14 at 10:26
@FabrizioCalderan: Are you serious? Also, would one use `goto` in JavaScript? — Bergi, Jan 14 '14 at 12:21
@Bergi what you can technically do is not what you actually would do. I thought I were clear. It's a solution but not necessarily a good solution (I would never use) - that's the reason I wrote a comment instead of an answer. — Fabrizio Calderan, Jan 14 '14 at 12:23
@FabrizioCalderan: Sure, but I'd be really interested in how it is technically possible to use `goto` in JavaScript. I've never heard of that? — Bergi, Jan 14 '14 at 12:25
... @Bergi I must had dead hamsters in my mind when I thought about a goto approach when I was actually thinking about labelled statement. (*Ok, it's all fine. Breath!*) — Fabrizio Calderan, Jan 14 '14 at 12:30
@Fabrizio: Ah, right, I love these :-) Unfortunately they don't work across function boundaries. — Bergi, Jan 14 '14 at 13:03

score 16 · Accepted Answer · answered Jan 14 '14 at 12:20

16

what do i need to do here to jump in to the fail handler?

Don't use done, but then to map over the result of the promise. By returning a rejected promise you can "throw" an error and reject the resulting promise, so that your fail handler is executed.

$.ajax(…)
  .then(function(data, status, jqxhr){
    if (data.error)
      return $.Deferred().reject(data.error);
    else
      return data; // if you want to return multiple arguments, you'd use
                   // $.Deferred().resolve(data, status, jqxhr);
  })
  .done(function(data) {
    …
  })
  .fail(function(jqxhr, status, err){
    …
  });

answered Jan 14 '14 at 12:20

Bergi

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i knew, it had to be possible! thanks. i've came across the `then` handler, but never quite understood its purpose. – lordvlad Jan 14 '14 at 15:41
But when we return new `$.Deferred()` object, we loose access to `.abort()` method `jqXHR` has? `$.Deferred()` object doesn't have it. – Nik Sumeiko Mar 15 '16 at 12:02
@manakor: You always loose that when you use `then`, this doesn't have anything to do with the callback return value. if you need `abort`, store a reference to the `jqXHR` object before chaining promise callbacks to it. – Bergi Mar 15 '16 at 16:17

Can I force jQuery Deferred/Ajax to execute fail handler after it has been resolved?

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