Promises

in Angular JS

What is a Promise?

A promise represents the result of

an asynchronous operation

AN async Experience

JS Async Operations

setTimeout/setInterval

XmlHttpRequest (AJAX)

Web Workers

Element Creation/OnLoad

Generators

Promise Facts

A Promise represents a task that will finish in the future
A Promise is a representation of an asynchronous activity
A Promise is an instance with three methods

then()
catch()
finally()

A Promise will eventually be resolved or rejected

A promise is in one of three different states

* Immutable

AngularJS Deferred API

Implemented using the $q service

Typical Use Case


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

    doSomethingAsync( function( result ) {
        deferred.resolve( result );
    } );

    return deferred.promise;
}

AngularJS Promise API

Result of deferred.promise


var p = myPromise();

    p.then( success, error, notify )
    p.catch( error )    
    p.finally ( callback )

Code Examples

GitHub: github.com/Transcordia/ng-meetup