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Handling Promises with $q in Angular JS

Old way of async operations

[code lang="javascript"]
function getCurrentUser(callback)

//Let assume if you have two functions as below
//function one
//some task with user
//function two
//some task with permissions

//If you need this both results simultaneously (Serialized)
//you can use as below as for old method
//do what you want with users and permissions
//But it contains following issues
//[1] Not Parallelizable
//[2] Not Composable
//[3] Not Dynamic (have to define the structure at runtime)
Better way if you go with Angular JS is service implementation. Its as below;

[code lang="javascript"]
//Then better way is $q
//Service implemenation as below
function getCurrentUser(){
//define deferred
//this is one time use object
var deferred = $q.defer();
//resolve object into deferred
//return promise
return deferred.promise;
//Calling it, some what different other than old method
//do tasks with user
//Async call

//How to make two functions parallelizable
//returns of user
var user=responses[0];
//returns of permissions
var permissions=responses[1];

//This will call defined methods parallel
//Wait for both methods, without moving to next in program flow
//$q.all doing this magic for us

//Following have been separated because to enforce separation of notifier and receiver

deferred.resolve() //notifier (mostly in service side)
promise.then() //receiver (mostly in controller side)

// Some more functions we getting as below
// [1] Send errors like below by notifier
// [2] Send progress updates

// Receiver implementation for above as below
// to do when Success
//to do when failure
//progress (i.e called 0 or more times)

//Can be used for client side caching

var chachedMovies//will store cached movies
,p//promise that returns when same request called while helper function is executing;

//return cahedMovies else call helper to get data
return $q.when(cachedMovies || p || helper());

//helper function
function helper(){
var deffered=$q.deffer();
//return the loaded values if this function called while http GET is processing
p = deffred.promise;
return deferred.promise;


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