Promises and Deferreds/Futures in Ext JS?

[Jan (HL)]

All those pages seem quite opaque in what actually happens.

Can you post some possible example of what you would like to happen?

// Proposal
var gridStore, detailsStore, tree, grid, form;
tree.on('click', function(tree, record){
  var promise = gridStore.load({id : record.get('id')});
  promise.success(detailsStore.load).success(form.update).failure(form.showError);
});

// instead of something like this.
tree.on('click', function(tree, record){
  gridStore.load({
    id : record.get('id'), 
    callback : function(r, o, success){
      if (success) {
        detailsStore.load({
          callback:function(r, o, success){
            if (success) {
              form.update(record);
            } else {
              form.showError();
            }
          }
        });
      } else {
        form.showError();
      }
    }
  });
}); 

It's not just callbacks. It is a different way of dispatching events. The real problem I see is the challenge of Sencha to provide an api which *is* deferable. Without chaining support (like jQuery) it is useless.

Again, an example of jQuery promise implementation:

var ajaxPromise = $.ajax('myurl').done(function(response){
  console.info("the response: " + response);
}).fail(function(){
  console.warn(arguments);
});
// oops, I need additional callbacks?
ajaxPromise.done(function(){
  console.info('done!!');
}).always(function(){
  console.log("whatever happend, I'm here");
}); 

[jefftrull]

One of the main uses for this feature is to save coders from callback spaghetti hell. Instead of deeply nested success/failure callback code you describe a series of operations as objects and then compose them. The jQuery implementation is pretty nice and is covered in detail here: http://net.tutsplus.com/tutorials/javascript-ajax/wrangle-async-tasks-with-jquery-promises/

ExtJS is nearly always ahead of the curve in terms of good design practices, so I'm surprised not to see something like this in there yet.

[StevenW]

the fact that sencha is completely clueless about promises/futures and think they're just callbacks is absolutely disconcerting to me.

[walter.rumsby]

It's worth noting that jQuery's implementation isn't a 100% faithful implementation of Promises - see You're Missing the Point of Promises for more.

[Greg Arnott]

I know this is a little late, but for reference.
A great article by Matt Goldspink "Promises in Ext.js and Sencha Touch":
http://www.mattgoldspink.co.uk/2013/...-sencha-touch/