[AngularJS] 5 simple ways to speed up your AngularJS application

Nowdays, Single page apps are becoming increasingly popular among the fornt-end developers. It is the time to say goodbye with refreshing the whole page due to clicking on a single link. It helps to speed up out web application and improve our use experience. Today we'd talk about how to speed up your AngularJS application. This article is based on AngularJS 1.3.x version.

1. Disabling the debug info

---

When you use directive, Angular adds some additional debug information to the DOM.

Javascript:

app.controller('AppController',  function () {
  this.appCtrl = this;

  appCtrl.message = "Hello World!";
});

HTML:

<p>{{appCtrl.message}}</p>

Once compiled, we get something like this:

<p class="ng-binding">Hello World!</p>

This debug info is super useful when you debuggin because the tools like Protractor and Batarang which can rely on this information. However, great things always come with cost. When our project comes to production, those information is useless to users. And additional properties and classes that are added to the DOM also come with a performance cost depending on how much is stored on the scope and DOM operations are expensive anyway.

AngularJS 1.3 enables us to switch those debug information, what you need to do to disable the debug info:

app.config(function( $compileProvider ) {

    $compileProvider.debugInfoEnabled(false);
});

To enable it again, you can do in console:

angular.reloadWithDebugInfo();

2. Use $applyAsync

---

Configure $http service to combine processing of multiple http responses received at around the same time via $rootScope.$applyAsync. This can result in significant performance improvement for bigger applications that make many HTTP requests concurrently (common during application bootstrap) [1].

Sinlge $http request triggers $digest() which can help to update application model and DOM. If you have many $http requests triggered almost at the same time and each request will run $digest() which cost a lot.

The idea to use $applyAsync is to compile multiple $http requets into one $digest. We show how to use this here:

app.config(function($httpProvider) {

    $httpProvider.useApplyAsync(true);
});

3. Using one time binding

---

AngularJS comes up with two way binding which is cool because you don't need to set up any event listen, it helps you to update the model automaticlly. But, as we said, great thing comes with cost.  In order to make databinding possible, Angular uses $watch APIs to observe model mutations on the scope. Imaging if there is too many watcher, your application become heavy and slow. This is why we need one-time binding. One-time expressions will stop recalculating once they are stable, which happens after the first digest.

You can see the demo here: http://jsbin.com/dijeno/9/edit?html,css,js,output

The way to use one time binding is quite simple, from our first simple of AppController, we know that everytime appCtrl.message changes, {{appCtrl.message}} will also change. So if we apply the one-time expression to our example above, we change this:

<p>{{::appCtrl.message}}</p>

4. Using lazy loading

---

Lazy loading is very useful when you have a large application which needs to load hundred files. And among those hundred files, there is only 10% files whcih are needed to bootstrap your applcation and the other 90% are only useful in the running time. So, in order to speed up, you don't want those 90% files loaded when the boostrap time. That is the place where lazy loading comes in to handy.

There are many ways to do lazy loading, for example RequireJS, the one which I often use is called ocLazyLoad. It is quite easy to use with AngularJS.

What you need to do first is install ocLazyLoad:

bower install oclazyload

Then inject into the application dependency:

var app = angular.module("demo", ["oc.lazyLoad"])

Javascript: When you click on the AppCtrl, we want to load everything related to the store module.

    app.controller("AppCtrl", function($ocLazyLoad) {

        var app = this;
        app.click = function() {
            $ocLazyLoad.load({
                name: "store",
                files: [
                    "app/store/store.js",
                    "app/store/store.tpl.html",
                    "app/css/store.css"
                ]
            })
        }
    })

5. Resolve data beforehand

---

Let see two parts of code first, then talk about why resolve is good.

Controller Way:

function MainCtrl(SomeService) {

    var mainCtrl= this;

    // unresolved
    mainCtrl.something;

    // resolved asynchronously
    SomeService.doSomething().then(function(response) {
        mainCtrl.something = response;
    });

}

angular.module('app', [])
    .controller('MainCtrl', MainCtrl);

Route Resolve:

// config with resolve pointing to relevant controller
function config ($routeProvider) {
  $routeProvider
  .when('/', {
    templateUrl: 'views/main.html',
    controller: 'MainCtrl',
    controllerAs: 'main',
    resolve: MainCtrl.resolve
  });
}
// controller as usual
function MainCtrl (SomeService) {
  // resolved!
  this.something = SomeService.something;
}
// create the resolved property
MainCtrl.resolve = {
  doSomething: function (SomeService) {
    return SomeService.doSomething();
  }
};

angular
  .module('app')
  .controller('MainCtrl', MainCtrl)
  .config(config);

For controller activate:

• Views load right away
• The Service code executes after the controller code
• Animation can be shown during the view transition

For route resolve

• The code executes before the route via a promise
• Resolve makes the new view wait for the route to resolve
• Animation can be shown before the resolve and through the view transition

　　

Resolve happens before your controller will instantiate, and your template will load and everything will set up. It gives users a felling that they can wait less time to get the interface updated, because all the data are already resolved (parpared) for interface to use.