Question

I’m doing an ajax call that can return {status: ok} or {status: error} along with other data.

I’d like to do a .then(doneFilter) that would check the status member and then modify things such that the Deferred now will resolve only if the status was ok.

I’m not sure of the syntax for that. Could someone write me an example?

Answer 1

I think that you want to modify the ajax deferred itself to trigger different callbacks based upon the return state. You can’t because Promise objects can be resolved only once. Look at this example:

var fai = $.Deferred();
fai.then(function () {
    fai.reject();
    console.log(fai.state());
}).done(function () {
    console.log(fai.state()); 
});
fai.resove();

http://jsfiddle.net/ExplosionPIlls/QreYY/

The chain of events would be calling .resolve, and then the .then callback. .then calls .reject. However, if you run this you will see that the state after the .reject call is still “resolved,” and the .done callback gets triggered.

That is to say if your ajax request succeeds it will already be set to the .resolved state and you can’t undo that.

Instead, you can do something like this, which I think is simpler anyway:

$.ajax(...).done(function (json) {
   if (json && json.status == 'ok') {
      //handle success right here
   }
   else {
      //handle failure right here
   }
});