Angular Performance: Your App at the Speed of Light

In this talk, you’ll get to know common performance pitfalls in Angular applications and learn how to avoid them. We’ll have a look at different change detection strategies and ChangeDetectorRef, Zone.js and NgZone. Let’s make your Angular app blazing fast!

Transcript

1. Angular Performance Your App at the Speed of Light Christian Liebel @christianliebel Consultant
2. Don’t over-optimize. Angular Performance Your App at the Speed of Light First Rule
3. Angular Performance Your App at the Speed of Light Change Detection Basics
4. Hi Angular! Basics // app.component.html <h1>Hi {{ title }}!</h1> // app.component.ts @Component({ /* … */ }) export class AppComponent { title = 'Angular'; } Angular Performance Your App at the Speed of Light Change Detection
5. Basics // app.component.html <h1>Hi {{ title }}!</h1> <button (click)="update()"> Update </button> // app.component.ts @Component({ /* … */ }) export class AppComponent { title = 'Angular'; update() { this.title = 'Foo'; } } Angular Performance Your App at the Speed of Light Change Detection Hi Foo! Hi Angular! Update
6. Basics Change detection… - is the magical part of Angular that makes data binding “just work” - is a very handy feature that helps a lot, but it can also work against you - is strongly related to Angular application performance Angular Performance Your App at the Speed of Light Change Detection
7. Component Tree AppComponent NavComponent ContentComponent ListComponent Angular Performance Your App at the Speed of Light Change Detection
8. Change Detector Tree AppComponent NavComponent ContentComponent ListComponent Angular Performance Your App at the Speed of Light Change Detection AppComponent CD NavComponent CD ContentComponent CD ListComponent CD CHANGE
9. Change Detector detectChanges() Called when an event has occured and bindings should be checked Angular Performance Your App at the Speed of Light Change Detection this.title = 'Foo'; <h1>Hi {{ title }}!</h1>
10. Per default, each change in your application leads to… - A single CD cycle - From top to bottom (all components) - Unidirectional (no cycles allowed) Angular Performance Your App at the Speed of Light Change Detection DEMO
11. Angular Performance Your App at the Speed of Light
12. First findings Reduce duration of a change detection cycle - Reduce amount of bindings (e.g. grids: virtual scrolling via CDK) - Avoid binding to (computationally intensive) getters or functions Keep CD cycle < 16 ms! Angular Performance Your App at the Speed of Light Change Detection
13. Profiling // main.ts platformBrowserDynamic().bootstrapModule(AppModule).then(module => enableDebugTools(module.injector.get(ApplicationRef).components[0])); Execute ng.profiler.timeChangeDetection() to measure the duration of a change detection run (500ms or 5 change detection cycles) Angular Performance Your App at the Speed of Light Change Detection DEMO
14. Angular Performance Your App at the Speed of Light
15. Angular Performance Your App at the Speed of Light Zone.js & NgZone
16. How to detect a change? AppComponent NavComponent ContentComponent ListComponent Angular Performance Your App at the Speed of Light Zone.js AppComponent CD NavComponent CD ContentComponent CD ListComponent CD CHANGE
17. A look at Angular’s dependencies "dependencies": { "@angular/common": "~8.2.3", "rxjs": "~6.4.0", "zone.js": "~0.9.1" }, Zone.js Your App at the Speed of Light Angular Performance
18. A Meta-Monkey Patch Zone.js setTimeout setInterval geolocation.getCurrentPosition XMLHttpRequest PromiseRejectionEvent requestAnimationFrame click focus mousemove addEventListener Your App at the Speed of Light Angular Performance
19. Execution Context Debugging Pending asynchronous tasks are known Profiling Measuring performance (Google Web Tracing Framework) Mocking/Testing Hooks beforeTask, … Zone.js Your App at the Speed of Light Angular Performance
20. NgZone Angular Performance Your App at the Speed of Light Zone.js current (global) zone NgZone Angular boot
21. NgZone NgZone catches asynchronous operations from the Angular app When no tasks are remaining for the current VM turn, the NgZone will trigger a change detection cycle (tick) Angular Performance Your App at the Speed of Light Zone.js NgZone setTimeout setInterval onclick Detect changes Detect changes Detect changes
22. Change Detection Trigger Angular Performance Your App at the Speed of Light Zone.js NgZone.onMicrotaskEmpty ApplicationRef.tick() view1.detectChanges() view2.detectChanges() viewN.detectChanges()
23. @Injectable() export class ApplicationRef { // … constructor (/* … */) { this._zone.onMicrotaskEmpty .subscribe( {next: () => { this._zone.run(() => { this.tick(); }); }}); } // … tick(): void { // … for (let view of this._views) { view.detectChanges(); } // … } // … } Angular Performance Your App at the Speed of Light https://github.com/angular/angular/blob/master/packages/core/src/application_ref.ts
24. Common Pitfalls Long CD cycles in combination with high-frequency events - mousemove - scroll - requestAnimationFrame - setInterval with short intervals (clocks!) Angular Performance Your App at the Speed of Light Zone.js DEMO
25. Angular Performance Your App at the Speed of Light
26. NgZone Zone.js current (global) zone NgZone mousemove Detect changes mousemove Detect changes mousemove Detect changes mousemove Detect changes Your App at the Speed of Light Angular Performance
27. NgZone Opt-Out constructor (ngZone: NgZone) { ngZone.runOutsideAngular(() => { // runs outside Angular zone, for performance-critical code ngZone.run(() => { // runs inside Angular zone, for updating view afterwards }); }); } Zone.js Your App at the Speed of Light Angular Performance ! View and model can get out of sync!
28. NgZone Zone.js current (global) zone NgZone mousemove mousemove mousemove mousemove Your App at the Speed of Light Angular Performance DEMO
29. Angular Performance Your App at the Speed of Light
30. Disable Patches (polyfills.ts) (window as any).__Zone_disable_requestAnimationFrame = true; // disable patch requestAnimationFrame (window as any).__Zone_disable_on_property = true; // disable patch onProperty such as onclick (window as any).__zone_symbol__BLACK_LISTED_EVENTS = ['scroll', 'mousemove']; // disable patch specified eventNames Angular Performance Your App at the Speed of Light Zone.js ! View and model can get out of sync!
31. Disable Zone (= disable async change detection!) platformBrowserDynamic().bootstrapModule(AppModule, { ngZone: 'noop' }); constructor(applicationRef: ApplicationRef) { applicationRef.tick(); // trigger CD yourself } Angular Performance Your App at the Speed of Light Zone.js ! View and model can get out of sync!
32. Angular Performance Your App at the Speed of Light Change Detection Strategies
33. Overview Default Uses Zone.js for detecting changes and updates bindings OnPush Restricts change detection to changes of @Input parameters Angular Performance Your App at the Speed of Light Change Detection Strategies AppComponent CD NavComponent CD ContentComponent CD ListComponent CD AppComponent CD NavComponent CD ContentComponent CD ListComponent CD OnPush
34. OnPush <my-component [foo]="bar"> </my-component> @Component({ selector: 'my-component', template: '{{ foo }}', changeDetection: ChangeDetectionStrategy.OnPush }) export class MyComponent { @Input() public foo: string; } Change detection only reacts to changes of @Input parameters Angular compares the values passed to an @Input parameter (newValue === oldValue). If you are passing objects, make sure to pass in new instances! Angular Performance Your App at the Speed of Light Change Detection Strategies ! View and model can get out of sync! DEMO
35. Angular Performance Your App at the Speed of Light
36. Angular Performance Your App at the Speed of Light Change Detector
37. OnPush & Detecting Changes What to do if a component changes unrelated to an @Input parameter? constructor(private dataService: DataService) {} ngOnInit() { this.dataService.updates$ .subscribe(newData => this.data = newData); // no update! } Angular Performance Your App at the Speed of Light Change Detector
38. ChangeDetectorRef constructor(cdRef: ChangeDetectorRef) {} A reference to the ChangeDetector of your component - detectChanges() - markForCheck() - detach() - checkNoChanges() - reattach() Angular Performance Your App at the Speed of Light Change Detector
39. markForCheck() Explicitly marks a component as dirty/changed (when using OnPush) Angular Performance Your App at the Speed of Light Change Detector AppComponent CD NavComponent CD ContentComponent CD ListComponent CD DIRTY AppComponent CD NavComponent CD ContentComponent CD ListComponent CD OnPush
40. markForCheck() constructor(private dataService: DataService, private cdRef: ChangeDetectorRef) {} ngOnInit() { this.dataService.updates$.subscribe(newData => { this.data = newData; this.cdRef.markForCheck(); }); } Angular Performance Your App at the Speed of Light Change Detector
41. Angular Performance Your App at the Speed of Light Async Pipe
42. Overview Takes observables or promises {{ data$ | async }} Waits for the observable to emit/promise to resolve and then displays the value Angular Performance Your App at the Speed of Light Async Pipe
43. Advantages For observables: - Async Pipe subscribes for you - Async Pipe takes care of unsubscribing from the observable - Async Pipe calls markForCheck for each update – perfect match for OnPush! Angular Performance Your App at the Speed of Light Async Pipe
44. Code @Injectable() @Pipe({name: 'async', pure: false}) export class AsyncPipe implements OnDestroy, PipeTransform { // … private _updateLatestValue(async: any, value: Object): void { if (async === this._obj) { this._latestValue = value; this._ref.markForCheck(); } } } Angular Performance Your App at the Speed of Light Async Pipe https://github.com/angular/angular/blob/master/packages/common/src/pipes/async_pipe.ts
45. Simplifying OnPush // component.ts data$: Observable<string>; constructor(dataService: DataService) { this.data$ = this.dataService.updates$; } // component.html {{ data$ | async }} Angular Performance Your App at the Speed of Light Async Pipe
46. Detaching from Change Detection Angular Performance Your App at the Speed of Light
47. Detaching Components changeDetector.detach(); changeDetector.reattach(); Angular Performance Your App at the Speed of Light Change Detector AppComponent CD NavComponent CD ContentComponent CD ListComponent CD AppComponent CD NavComponent CD ContentComponent CD ListComponent CD ! View and model can get out of sync!
48. Local Change Detection constructor(cdRef: ChangeDetectorRef) { cdRef.detach(); // detaches this view from the CD tree // cdRef.detectChanges(); // detect this view & children // cdRef.reattach(); } Angular Performance Your App at the Speed of Light Change Detector
49. Findings Reduce amount of change detection cycles - Disable Zone.js (not a good idea in most cases) - Opt-out of NgZone (for operations that should not affect bindings) - Disable Zone.js patches (in case you can’t opt-out, e.g. 3rd party libs) - ChangeDetectionStrategy.OnPush (good default, but be careful) - Local change detection via ChangeDetectorRef (for the few components that do not have to respond to changes from outside) Angular Performance Your App at the Speed of Light Change Detector
50. Runtime Performance 1. Don’t over-optimize 2. Reduce duration of a change detection cycle - Reduce amount of bindings - Avoid binding to (computationally intensive) getters or functions 3. Reduce amount of change detection cycles - Disable zone - NgZone - Zone.js patches - ChangeDetectorRef - ChangeDetectionStrategy Angular Performance Your App at the Speed of Light Cheat Sheet
51. Thank you for your kind attention! Christian Liebel @christianliebel christian.liebel@thinktecture.com