Combines multiple promises into a single promise that is resolved when all of the input promises are resolved.

defer: 推迟做某事

defer.promise.then(successCallback, errorCallback, notifyCallback)：许诺要做的事

resolve：决定现在做某事,

Awaiting multiple promises running in parallel

Assume having to call different backend services to collect data. The application can only continue once all the data has been successfully collected (success) or if at least one of the server call fails (failure). For maximum performance all tasks shall run in parallel. To await multiple tasks running in parallel the $q service offers us the all function. The all function in turn returns a promise. The promise is fulfilled if all parallel running tasks are fulfilled or the promise fails if at least one of the tasks fails. If we have three asynchronous tasks the code looks like this.

 Read More: 

http://lostechies.com/gabrielschenker/2014/02/04/angularjspart-11-promises/

var app = angular.module("app", []);

app.controller("AppCtrl", function ($q, $timeout) {
    var one = $q.defer();
    var two = $q.defer();
    var three = $q.defer();

    function success(data){

        console.log(data);
    }

/* Not necessary to be here if use $q.all([promises array]).then(success)
    one.promise.then(success); 
    two.promise.then(success);
    three.promise.then(success);
*/

    var all = $q.all([one.promise, two.promise, three.promise]);
    all.then(success);
    
    $timeout(function () {
            one.resolve("one is done");
        },
            Math.random() * 1000);

    $timeout(function () {
            two.resolve("two is done");
        },
            Math.random() * 1000);
    $timeout(function () {
            three.resolve("three is done");
        },
            Math.random() * 1000);


})