Small Overview about Angular Promises?

Question

Promises in AngularJS are provided by the built-in $q service. They provide a way to execute asynchronous functions in series by registering them with a promise object.

A service that helps you run functions asynchronously, and use their return values (or exceptions) when they are done processing.

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

Methods:

• Resolve(value)
• Reject(reason)
• Notify(notify)

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

Methods:

• then()
• catch()
• finally()

$q is integrated with the $rootScope.Scope Scope model observation mechanism in angular, which means faster propagation of resolution or rejection into your models and avoiding unnecessary browser repaints, which would result in flickering UI.

Example Code:

_{var deferred = $q.defer();
var promise = deferred.promise;
 
promise.then(function success(data) {
  console.log('Success!', data);
}, function error(msg) {
  console.error('Failure!', msg);
});
 
deferred.reject('We failed :(');}

Video about Angular Services