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Angular Performance: Your App at the Speed of Light

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!

Christian Liebel

August 30, 2019
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  1. Angular Performance
    Your App at the Speed of Light
    Christian Liebel
    @christianliebel
    Consultant

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

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

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  4. 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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  5. 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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  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

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

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  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

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  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'; Hi {{ title }}!

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  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

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  11. Angular Performance
    Your App at the Speed of Light

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  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

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  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

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  14. Angular Performance
    Your App at the Speed of Light

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

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  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

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  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

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  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

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  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

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

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  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

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  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()

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  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

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  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

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  25. Angular Performance
    Your App at the Speed of Light

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  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

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  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!

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  28. 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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  29. Angular Performance
    Your App at the Speed of Light

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  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!

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  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!

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

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  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

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  34. 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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  35. Angular Performance
    Your App at the Speed of Light

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  36. Angular Performance
    Your App at the Speed of Light
    Change Detector

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  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

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  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

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  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

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  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

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  41. Angular Performance
    Your App at the Speed of Light
    Async Pipe

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  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

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  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

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  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

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

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  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!

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  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

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  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

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  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

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

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