Promises API

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If you aren’t familiar with Promises, perhaps the Wikipedia definition will help:

In computer science, future, promise, and delay refer to constructs used for synchronizing in some concurrent programming languages. They describe an object that acts as a proxy for a result that is initially unknown, usually because the computation of its value is yet incomplete.

Put another way, a Promise represents a future value that will eventually be returned asynchronously. In the JavaScript world, the folks at CommonJS have proposed a specification called Promises/A, which is what the DeftJS Promise API is modeled upon.

In it's most basic and common form, a method will create and return a Promise like this:

// A method which uses a Store and returns a Promise
loadCompanies: function() {
  var deferred = Ext.create('Deft.Deferred');
  
  this.companyStore.load({

    callback: function(records, operation, success) {
      if (success) {
        return deferred.resolve(records);
      } else {
        return deferred.reject("Error loading Companies.");
      }
    }

  });
  
  return deferred.promise;
}

The method which calls the above code and works with the returned Promise might look like:

// Using a Promise returned by another object.
loadCompanies: function() {

  this.companyService.loadCompanies().then({
    success: function(records) {
      // Do something with result.
    },
    failure: function(error) {
      // Do something on failure.
    }
  }).always(function() {
    // Do something whether call succeeded or failed
  });

}

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