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Angular Performance Your App at the Speed of Light Christian Liebel @christianliebel Consultant

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Don’t over-optimize. Angular Performance Your App at the Speed of Light First Rule

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Angular Performance Your App at the Speed of Light Change Detection Basics

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Hi Angular! Basics // app.component.html

Hi {{ title }}!

// app.component.ts @Component({ /* … */ }) export class AppComponent { title = 'Angular'; } Angular Performance Your App at the Speed of Light Change Detection

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Basics // app.component.html

Hi {{ title }}!

Update // 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

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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

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Component Tree AppComponent NavComponent ContentComponent ListComponent Angular Performance Your App at the Speed of Light Change Detection

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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

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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';

Hi {{ title }}!

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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

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Angular Performance Your App at the Speed of Light

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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

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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

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Angular Performance Your App at the Speed of Light

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Angular Performance Your App at the Speed of Light Zone.js & NgZone

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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

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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

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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

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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

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NgZone Angular Performance Your App at the Speed of Light Zone.js current (global) zone NgZone Angular boot

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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

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Change Detection Trigger Angular Performance Your App at the Speed of Light Zone.js NgZone.onMicrotaskEmpty ApplicationRef.tick() view1.detectChanges() view2.detectChanges() viewN.detectChanges()

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@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

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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

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Angular Performance Your App at the Speed of Light

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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

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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!

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NgZone Zone.js current (global) zone NgZone mousemove mousemove mousemove mousemove Your App at the Speed of Light Angular Performance DEMO

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Angular Performance Your App at the Speed of Light

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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!

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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!

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Angular Performance Your App at the Speed of Light Change Detection Strategies

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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

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OnPush @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

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Angular Performance Your App at the Speed of Light

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Angular Performance Your App at the Speed of Light Change Detector

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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

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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

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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

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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

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Angular Performance Your App at the Speed of Light Async Pipe

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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

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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

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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

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Simplifying OnPush // component.ts data$: Observable; constructor(dataService: DataService) { this.data$ = this.dataService.updates$; } // component.html {{ data$ | async }} Angular Performance Your App at the Speed of Light Async Pipe

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Detaching from Change Detection Angular Performance Your App at the Speed of Light

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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!

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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

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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

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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

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Thank you for your kind attention! Christian Liebel @christianliebel [email protected]