// for the purpose of this example let's assume that variables `$q` and `okToGreet`
// are available in the current lexical scope (they could have been injected or passed in).

function asyncGreet(name) {
  var deferred = $q.defer();

  setTimeout(function() {
    deferred.notify('About to greet ' + name + '.');

    if (okToGreet(name)) {
      deferred.resolve('Hello,' + name + '!');
    } else {
      deferred.reject('Greeting ' + name + ' is not allowed.');
    }
  },1000);

  return deferred.promise;
}

var promise = asyncGreet('Robin Hood');
promise.then(function(greeting) {
  alert('Success: ' + greeting);
},function(reason) {
  alert('Failed: ' + reason);
},function(update) {
  alert('Got notification: ' + update);
});

The Deferred API

A new instance of deferred is constructed by calling$q.defer().

The purpose of the deferred object is to expose the associated Promise instance as well as APIs that can be used for signaling the successful or unsuccessful completion,as well as the status of the task.

Methods

• resolve(value)– resolves the derived promise with thevalue. If the value is a rejection constructed viareject,the promise will be rejected instead.
• rejectreason)– rejects the derived promise with thereason. This is equivalent to resolving it with a rejection constructed viareject.
• notify)- provides updates on the status of the promise's execution. This may be called multiple times before the promise is either resolved or rejected.

Properties

• promise –{Promise}– promise object associated with this deferred.

The Promise API

A new promise instance is created when a deferred instance is created and can be retrieved by callingdeferredpromise.

The purpose of the promise object is to allow for interested parties to get access to the result of the deferred task when it completes.