Angular performance slides

Small computers, big performance:
Optimize your Angular

Speakers
David Barreto
Andrew Smith

Agenda
1. Ahead of Time Compilation
2. Lazy Loading
3. Change Detection
4. Memory Leaks
5. Server Side Rendering

Rangle Academy
Goal and Structure:
Program to share knowledge within the company
It follows a "workshop" structure
Usually 2 hours long
Covers hard and soft skills
Some workshops available:
Webpack
React
React Native
Google Analytics
Unit Testing
Introduction to Payment Gateways
Continuous Delivery to Production
Conflict Management

About the Demo App
Characteristics:
Built using Angular 2.4.1
Uses Angular CLI beta-26
Redux store with ngrx
Tachyons for CSS
Server side rendering with Universal
All the numbers shown are based on:
Low end device emulation (5x slowdown)
Good 3G connection emulation

Ahead of Time Compilation (AoT)

Compilation Modes
Just in Time Compilation (JiT):
Compilation performed in the browser at run time
Bigger bundle size (includes the compiler)
Takes longer to boot the app
$ ng serve --prod
Ahead of Time Compilation (AoT):
Compilation performed in the server at build time
Smaller bundle size (doesn't include the compiler)
The app boots faster
$ ng serve --prod --aot

JiT vs AoT in Demo App (Prod + Gzip)
CSS files are included in the "other js files"
File Size (JiT) Size (AoT)
main.bundle.js 6.4 KB 23.9 KB
vendor.bundle.js 255 KB 158 KB
other js files 48.7 KB 49.6 KB
Total Download 306 KB 231.5 KB
AoT goals (from the ):docs
Faster rendering => Components already compiled
Fewer async request => Inline external HTML and CSS
Smaller bundle size => No compiler shipped
Detect template errors => Because they can
Better security => Prevents script injection attack

Boot Time Comparison
Event Time (JiT) Time (AoT)
DOM Content Loaded 5.44 s 3.25 s
Load 5.46 s 3.27 s
FMP 5.49 s 3.30 s
DOM Content Loaded:
The browser has finished parsing the DOM
jQuery nostalgia => $(document).ready()
Load: All the assets has been downloaded
First Meaningful Paint (FMP):
When the user is able to see the app "live" for the first time
(Show browser profile for both modes)

What is Lazy Loading?
Ability to load modules on demand => Useful to reduce the app startup time
(Compare branches no-lazy-loading vs normal-lazy-loading )

Bundle Sizes Comparison (Prod + AoT)
File Size (No LL) Size (LL)
main.bundle.js 23.9 KB 17.4 KB
vendor.bundle.js 158 KB 158 KB
other js files 49.6 KB 49.6 KB
Initial Download 231.5 KB 225 KB
0.chunk.js - 9.1 KB
Total Download 231.5 KB 234.1 KB
Webpack creates a "chunk" for every lazy loaded module
The file 0.chunk.js is loaded when the user navigates to admin
The initial download size is smaller with LL
The total size over time is bigger with LL because of Webpack async loading
The eﬀect of LL start to be noticeable when the app grows

Boot Time Comparison (Prod + AoT)
Event Time (No LL) Time (LL)
DOM Content Loaded 3.25 s 3.11 s
Load 3.27 s 3.25 s
FMP 3.30 s 3.16 s
Not much diﬀerence for an small app
Just one lazy loaded module with a couple of components
The impact is noticeable for big apps

How to Enable Lazy Loading? (1/4)
Step 1: Organize your code into modules
$ tree src/app -L 1
src/app
├── admin/
├── app-routing.module.ts
├── app.component.ts
├── app.module.ts
├── core/
├── public/
└── shared/
CoreModule provides all the services and the Redux store
SharedModule provides all the reusable components, directives or pipes
PublicModule provides the components and routing of the public section of the app
AdminModule provides the components and routing of the private section of the app
AppModule root module
(Show modules in the IDE)

How to Enable Lazy Loading (2/4)
Step 2: Create a routing module for lazy loaded module
const routes: Routes = [{
path: '',
component: AdminComponent,
children: [
{ path: '', redirectTo: 'list', pathMatch: 'full' },
{ path: 'list', component: WorkshopListComponent },
{ path: 'new', component: WorkshopEditorComponent },
{ path: 'edit/:id', component: WorkshopEditorComponent },
]
}];
@NgModule({
imports: [ RouterModule.forChild(routes) ],
exports: [ RouterModule ],
})
export class AdminRoutingModule {}
Always use the method forChild when importing the RouterModule
Avoids duplication of services in the child injector

Step 3: Define a child <router-outlet> to render child routes
@Component({
selector: 'rio-admin',
template: `
<nav>
<a routerLink="./list">List Workshops</a>
<a routerLink="./new">Create Workshop</a>
</nav>
<router-outlet></router-outlet>
`,
})
export class AdminComponent {}

Step 4: Use the property loadChildren to lazy load the module
export const routes: Routes = [{
path: 'admin',
loadChildren: 'app/admin/admin.module#AdminModule',
canActivate: [ AuthGuardService ],
}];
@NgModule({
imports: [ RouterModule.forRoot(routes) ],
})
export class AppRoutingModule {}
Only in the root module use the forRoot method of RouterModule
Never import a lazy loaded in this file, use a string as reference
The path of loadChildren is not relative to the file, but to the index.html file
(Show routes in the IDE and URL structure of the app)

Preloading
(Compare branches normal-lazy-loading vs master )

Enable Preloading
Define the property preloadingStrategy in the root module routing
import { PreloadAllModules } from '@angular/router';
export const routes: Routes = [ ... ];
@NgModule({
imports: [
RouterModule.forRoot(routes, {
preloadingStrategy: PreloadAllModules
})
],
})
export class AppRoutingModule {}

What's Change Detection (CD)?
It's a mechanism to keep our "models" in sync with our "views"
Change detection is fired when...
The user interacts with the app (click, submit, etc.)
An async event is completed (setTimeout, promise, observable)
When CD is fired, Angular will check every component starting from the top once.

Change Detection Strategy: OnPush
Angular oﬀers 2 strategies:
Default: Check the entire component when CD is fired
OnPush: Check only relevant subtrees when CD is fired
OnPush Requirements:
Component inputs ( @Input ) need to be immutable objects
@Component({
selector: 'rio-workshop',
templateUrl: './workshop.component.html',
changeDetection: ChangeDetectionStrategy.OnPush
})
export class WorkshopComponent {
@Input() workshop: Workshop;
@Input() isSummary = false;
}
View Example

Summary
What to do?
Apply the OnPush change detection on every component*
Never mutate an object or array, always create a a new reference ( )blog
// Don't
let addPerson = (person: Person): void => {
people.push(person);
};
// Do
let addPerson = (people: Person[], person: Person): Person[] => {
return [ ...people, person ];
};
Benefits:
Fewer checks of your components during Change Detection
Improved overall app performance

What's Memory Leak?
The increase of memory usage over time

What Causes Memory Leaks in Angular?
Main Source => Subscriptions to observables never closed
@Injectable()
export class WorkshopService {
getAll(): Observable<Workshop[]> { ... }
}
@Component({
selector: 'rio-workshop-list',
template: `
<div *ngFor="let workshop of workshops">
{{ workshop.title }}
</div>`
})
export class WorkshopListComponent implements OnInit {
...
ngOnInit() {
this.service.getAll().subscribe(workshops => this.workshops = workshops);
}
}

Manually Closing Connections
Before the element is destroyed, close the connection
@Component({
template: `
</div>`
})
export class WorkshopListComponent implements OnInit, OnDestroy {
...
ngOnInit() {
this.subscription = this.service.getAll()
.subscribe(workshops => this.workshops = workshops);
}
ngOnDestroy() {
this.subscription.unsubscribe();
}
}

The async Pipe
It closes the connection automatically when the component is destroyed
@Component({
template: `
<div *ngFor="let workshop of workshops$ | async">
</div>`
})
ngOnInit() {
this.workshops$ = this.service.getAll();
}
}
This is the recommended way of dealing with Observables in your template!

The Http Service
Every method of the http services ( get , post , etc.) returns an observable
Those observables emit only one value and the connection is closed automatically
They won't cause memory leak issues
@Component({
template: `
</div>`
})
...
ngOnInit() {
this.http.get('some-url')
.map(data => data.json())
}
}

Emit a Limited Number of Values
RxJs provides operators to close the connection automatically
Examples: first() and take(n)
This won't cause memory leak issues even if getAll emits multiple values
@Component({
template: `
</div>`
})
ngOnInit() {
this.service.getAll().first()
}
}

Angular Universal
Provides the ability to pre-render your application on the server
Much faster time to first paint
Enables better SEO
Enables content preview on social networks
Fallback support for older browsers
Use the as the base of your applicationuniversal-starter

What's Included
Suite of polyfills for the server
Server rendering layer
Preboot - replays your user's interactions after Angular has bootstrapped
State Rehydration - Don't lose your place when the application loads

Boot Time Comparison (Client vs Server)
Both environments include previous AoT and Lazy Loading enhancements
Event Time (Client) Time (Server)
DOM Content Loaded 3.11 s 411 ms
Load 3.25 s 2.88 s
FMP 3.16 s ~440 ms
*Times are on mobile over 3G

Universal Caveats
Cannot directly access the DOM
constructor(element: ElementRef, renderer: Renderer) {
renderer.setElementStyle(element.nativeElement, ‘font-size’, ‘x-large’);
}
Current solutions only cover Express and ASP.NET servers
Project will be migrated into the core Angular repo for v4

Performance Changes
Event JiT AoT Lazy Loading SSR
DOM Content Loaded 5.44 s 3.25 s 3.11 s 411 ms
Load 5.46 s 3.27 s 3.25 s 2.88 s
FMP 5.46 s 3.30 s 3.16 s ~440 ms
% Improvement (FMP) 39.6% 4.3% 86.1%
*Times are on mobile over 3G

Slides
https://github.com/rangle/angular-performance-meetup

Angular performance slides

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