I have a question about dojo/Deferred. I'll start with the question, then go into more detail about what I'm doing:

Is there a way to execute the same lines of code regardless of the oute of the deferred, sort of like a finally block in a try...catch statement? From what I've read, it doesn't seem like there is, but maybe I'm understanding the documentation wrong and wanted to verify that with the SO munity.

Here's what I'm doing:

In Dojo 1.9 (also works in 1.8), I instantiate a dojox.widget.Standby (a loading overlay) for a ContentPane before loading some data. Once the deferred call has pleted, I want to hide my overlay as shown below:

standby = new Standby({
    ... // standby props
});
this.addChild(standby);
standby.show();

queryResults = grid.store.query({
    ... // query props
});
queryResults.then(function (results) {
    if (results) {
        ... // do something
    }

    standby.hide();
}, function (error) {
    ... // handle error

   standby.hide();
});

This works fine; however, presumably, I could have some process to be implement after the deferred pletes that takes up several lines of code instead of just a single line and I wouldn't want to duplicate those lines of code. An alternative would be to create a private function and just call it with a one-liner in each block, but if there's a better way, I'd rather take that route.

Thanks in advance!

I have a question about dojo/Deferred. I'll start with the question, then go into more detail about what I'm doing:

Is there a way to execute the same lines of code regardless of the oute of the deferred, sort of like a finally block in a try...catch statement? From what I've read, it doesn't seem like there is, but maybe I'm understanding the documentation wrong and wanted to verify that with the SO munity.

Here's what I'm doing:

In Dojo 1.9 (also works in 1.8), I instantiate a dojox.widget.Standby (a loading overlay) for a ContentPane before loading some data. Once the deferred call has pleted, I want to hide my overlay as shown below:

standby = new Standby({
    ... // standby props
});
this.addChild(standby);
standby.show();

queryResults = grid.store.query({
    ... // query props
});
queryResults.then(function (results) {
    if (results) {
        ... // do something
    }

    standby.hide();
}, function (error) {
    ... // handle error

   standby.hide();
});

This works fine; however, presumably, I could have some process to be implement after the deferred pletes that takes up several lines of code instead of just a single line and I wouldn't want to duplicate those lines of code. An alternative would be to create a private function and just call it with a one-liner in each block, but if there's a better way, I'd rather take that route.

Thanks in advance!

• javascript
• dojo
• promise
• deferred

Share Improve this question Follow edited Jun 27, 2013 at 17:48 Default 16.5k33 gold badges2828 silver badges3838 bronze badges asked Jun 27, 2013 at 14:54 DavidDavid 39344 silver badges1717 bronze badges

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3 Answers 3

Sorted by: Reset to default 5

You can use the always method of the Promises API to execute a function regardless of whether the underlying Deferred succeeds or fails.

queryResult
   .then(onSuccess, onFailure)
   .always(function() {
      standby.hide();
   });

This is a good question. A dojo/Deferred object will return another Deferred object when Deferred#then is called. This allows you to chain a differed with multiple callbacks that are fired in a serial order. Therefore, I believe you can do something like this:

queryResults.then(function (results) {
   if (results) {
       ... // do something
   }
}, function (error) {
    ... // handle error
}).then(function(data){
    // This will be fired with data returned from the previous callback.
    standby.hide();
});

You can see this example fiddle that illustrates a similar, albeit simple, use case where regardless of if the Deferred is rejected or resolved, the callback to the second Deferred#then is fired after the initial error/success callback.

var deferred = new Deferred(); 
deferred.promise.always( function() { alert('ciao'); } );