perf: do not trigger change detection internally on mouseleave

src/lib/picker/category.component.ts

@@ -11,12 +11,11 @@ import {
   OnInit,
   Output,
   SimpleChanges,
-  ViewChild
+  ViewChild,
 } from '@angular/core';
 import { Observable, Subject } from 'rxjs';
 import { EmojiFrequentlyService } from './emoji-frequently.service';
 
-
 @Component({
   selector: 'emoji-category',
   template: `
@@ -34,9 +33,7 @@ import { EmojiFrequentlyService } from './emoji-frequently.service';
         </span>
       </div>
 
-      <div
-        *ngIf="virtualize; else normalRenderTemplate"
-      >
+      <div *ngIf="virtualize; else normalRenderTemplate">
         <div *ngIf="filteredEmojis$ | async as filteredEmojis">
           <ngx-emoji
             *ngFor="let emoji of filteredEmojis; trackBy: trackById"
@@ -53,7 +50,7 @@ import { EmojiFrequentlyService } from './emoji-frequently.service';
             [hideObsolete]="hideObsolete"
             [useButton]="emojiUseButton"
             (emojiOver)="emojiOver.emit($event)"
-            (emojiLeave)="emojiLeave.emit($event)"
+            (emojiLeaveOutsideAngular)="emojiLeaveOutsideAngular.emit($event)"
             (emojiClick)="emojiClick.emit($event)"
           ></ngx-emoji>
         </div>
@@ -82,31 +79,31 @@ import { EmojiFrequentlyService } from './emoji-frequently.service';
     </section>
 
     <ng-template #normalRenderTemplate>
-        <ngx-emoji
-          *ngFor="let emoji of emojisToDisplay; trackBy: trackById"
-          [emoji]="emoji"
-          [size]="emojiSize"
-          [skin]="emojiSkin"
-          [isNative]="emojiIsNative"
-          [set]="emojiSet"
-          [sheetSize]="emojiSheetSize"
-          [forceSize]="emojiForceSize"
-          [tooltip]="emojiTooltip"
-          [backgroundImageFn]="emojiBackgroundImageFn"
-          [imageUrlFn]="emojiImageUrlFn"
-          [hideObsolete]="hideObsolete"
-          [useButton]="emojiUseButton"
-          (emojiOver)="emojiOver.emit($event)"
-          (emojiLeave)="emojiLeave.emit($event)"
-          (emojiClick)="emojiClick.emit($event)"
-        ></ngx-emoji>
+      <ngx-emoji
+        *ngFor="let emoji of emojisToDisplay; trackBy: trackById"
+        [emoji]="emoji"
+        [size]="emojiSize"
+        [skin]="emojiSkin"
+        [isNative]="emojiIsNative"
+        [set]="emojiSet"
+        [sheetSize]="emojiSheetSize"
+        [forceSize]="emojiForceSize"
+        [tooltip]="emojiTooltip"
+        [backgroundImageFn]="emojiBackgroundImageFn"
+        [imageUrlFn]="emojiImageUrlFn"
+        [hideObsolete]="hideObsolete"
+        [useButton]="emojiUseButton"
+        (emojiOver)="emojiOver.emit($event)"
+        (emojiLeaveOutsideAngular)="emojiLeaveOutsideAngular.emit($event)"
+        (emojiClick)="emojiClick.emit($event)"
+      ></ngx-emoji>
     </ng-template>
   `,
   changeDetection: ChangeDetectionStrategy.OnPush,
   preserveWhitespaces: false,
 })
 export class CategoryComponent implements OnChanges, OnInit, AfterViewInit {
-  @Input() emojis: any[] | null = null
+  @Input() emojis: any[] | null = null;
   @Input() hasStickyPosition = true;
   @Input() name = '';
   @Input() perLine = 9;
@@ -130,12 +127,15 @@ export class CategoryComponent implements OnChanges, OnInit, AfterViewInit {
   @Input() emojiImageUrlFn?: Emoji['imageUrlFn'];
   @Input() emojiUseButton?: boolean;
   @Output() emojiOver: Emoji['emojiOver'] = new EventEmitter();
-  @Output() emojiLeave: Emoji['emojiLeave'] = new EventEmitter();
+  /**
+   * Note: the suffix is added explicitly so we know the event is dispatched outside of the Angular zone.
+   */
+  @Output() emojiLeaveOutsideAngular: Emoji['emojiLeave'] = new EventEmitter();
   @Output() emojiClick: Emoji['emojiClick'] = new EventEmitter();
   @ViewChild('container', { static: true }) container!: ElementRef;
   @ViewChild('label', { static: true }) label!: ElementRef;
   containerStyles: any = {};
-  emojisToDisplay: any[]  = []
+  emojisToDisplay: any[] = [];
   private filteredEmojisSubject = new Subject<any[] | null | undefined>();
   filteredEmojis$: Observable<any[] | null | undefined> = this.filteredEmojisSubject.asObservable();
   labelStyles: any = {};
@@ -188,13 +188,12 @@ export class CategoryComponent implements OnChanges, OnInit, AfterViewInit {
       minHeight: `${this.rows * (this.emojiSize + 12) + 28}px`,
     };
 
-    this.ref?.detectChanges();
+    this.ref.detectChanges();
 
     this.handleScroll(this.container.nativeElement.parentNode.parentNode.scrollTop);
   }
 
-
-  get noEmojiToDisplay():boolean{
+  get noEmojiToDisplay(): boolean {
     return this.emojisToDisplay.length === 0;
   }
 
@@ -222,7 +221,10 @@ export class CategoryComponent implements OnChanges, OnInit, AfterViewInit {
       const { top, height } = this.container.nativeElement.getBoundingClientRect();
       const parentHeight = this.container.nativeElement.parentNode.parentNode.clientHeight;
 
-      if (parentHeight + (parentHeight + this.virtualizeOffset) >= top && -height - (parentHeight + this.virtualizeOffset) <= top) {
+      if (
+        parentHeight + (parentHeight + this.virtualizeOffset) >= top &&
+        -height - (parentHeight + this.virtualizeOffset) <= top
+      ) {
         this.filteredEmojisSubject.next(this.emojisToDisplay);
       } else {
         this.filteredEmojisSubject.next([]);
@@ -248,13 +250,12 @@ export class CategoryComponent implements OnChanges, OnInit, AfterViewInit {
       return;
     }
 
-    let frequentlyUsed =
-      this.recent || this.frequently.get(this.perLine, this.totalFrequentLines);
+    let frequentlyUsed = this.recent || this.frequently.get(this.perLine, this.totalFrequentLines);
     if (!frequentlyUsed || !frequentlyUsed.length) {
       frequentlyUsed = this.frequently.get(this.perLine, this.totalFrequentLines);
     }
     if (!frequentlyUsed.length) {
-      return
+      return;
     }
     this.emojis = frequentlyUsed
       .map(id => {
@@ -266,7 +267,6 @@ export class CategoryComponent implements OnChanges, OnInit, AfterViewInit {
         return id;
       })
       .filter(id => !!this.emojiService.getData(id));
-
   }
 
   updateDisplay(display: 'none' | 'block') {

src/lib/picker/ngx-emoji/emoji.component.spec.ts

@@ -0,0 +1,33 @@
+import { ApplicationRef, Component } from '@angular/core';
+import { TestBed } from '@angular/core/testing';
+
+import { EmojiModule } from './emoji.module';
+
+describe('EmojiComponent', () => {
+  it('should trigger change detection whenever `emojiLeave` has observers', () => {
+    @Component({
+      template: '<ngx-emoji (emojiLeave)="onEmojiLeave()"></ngx-emoji>',
+    })
+    class TestComponent {
+      onEmojiLeave() {}
+    }
+
+    TestBed.configureTestingModule({
+      imports: [EmojiModule],
+      declarations: [TestComponent],
+    });
+
+    const fixture = TestBed.createComponent(TestComponent);
+    fixture.detectChanges();
+
+    const appRef = TestBed.inject(ApplicationRef);
+    spyOn(appRef, 'tick');
+    spyOn(fixture.componentInstance, 'onEmojiLeave');
+
+    const emoji = fixture.nativeElement.querySelector('span.emoji-mart-emoji');
+    emoji.dispatchEvent(new MouseEvent('mouseleave'));
+
+    expect(appRef.tick).toHaveBeenCalledTimes(1);
+    expect(fixture.componentInstance.onEmojiLeave).toHaveBeenCalled();
+  });
+});

src/lib/picker/ngx-emoji/emoji.component.ts

@@ -1,11 +1,17 @@
 import {
   ChangeDetectionStrategy,
   Component,
+  ElementRef,
   EventEmitter,
   Input,
+  NgZone,
   OnChanges,
+  OnDestroy,
   Output,
+  ViewChild,
+  inject,
 } from '@angular/core';
+import { EMPTY, Subject, fromEvent, switchMap, takeUntil } from 'rxjs';
 
 import { EmojiData } from './data/data.interfaces';
 import { DEFAULT_BACKGROUNDFN, EmojiService } from './emoji.service';
@@ -37,45 +43,48 @@ export interface EmojiEvent {
 @Component({
   selector: 'ngx-emoji',
   template: `
-    <button
-      *ngIf="useButton && isVisible"
-      type="button"
-      (click)="handleClick($event)"
-      (mouseenter)="handleOver($event)"
-      (mouseleave)="handleLeave($event)"
-      [attr.title]="title"
-      [attr.aria-label]="label"
-      class="emoji-mart-emoji"
-      [class.emoji-mart-emoji-native]="isNative"
-      [class.emoji-mart-emoji-custom]="custom"
-    >
-      <span [ngStyle]="style">
-        <ng-template [ngIf]="isNative">{{ unified }}</ng-template>
-        <ng-content></ng-content>
-      </span>
-    </button>
-
-    <span
-      *ngIf="!useButton && isVisible"
-      (click)="handleClick($event)"
-      (mouseenter)="handleOver($event)"
-      (mouseleave)="handleLeave($event)"
-      [attr.title]="title"
-      [attr.aria-label]="label"
-      class="emoji-mart-emoji"
-      [class.emoji-mart-emoji-native]="isNative"
-      [class.emoji-mart-emoji-custom]="custom"
-    >
-      <span [ngStyle]="style">
-        <ng-template [ngIf]="isNative">{{ unified }}</ng-template>
-        <ng-content></ng-content>
+    <ng-template [ngIf]="isVisible">
+      <button
+        *ngIf="useButton; else spanTpl"
+        #button
+        type="button"
+        (click)="handleClick($event)"
+        (mouseenter)="handleOver($event)"
+        [attr.title]="title"
+        [attr.aria-label]="label"
+        class="emoji-mart-emoji"
+        [class.emoji-mart-emoji-native]="isNative"
+        [class.emoji-mart-emoji-custom]="custom"
+      >
+        <span [ngStyle]="style">
+          <ng-template [ngIf]="isNative">{{ unified }}</ng-template>
+          <ng-content></ng-content>
+        </span>
+      </button>
+    </ng-template>
+
+    <ng-template #spanTpl>
+      <span
+        #button
+        (click)="handleClick($event)"
+        (mouseenter)="handleOver($event)"
+        [attr.title]="title"
+        [attr.aria-label]="label"
+        class="emoji-mart-emoji"
+        [class.emoji-mart-emoji-native]="isNative"
+        [class.emoji-mart-emoji-custom]="custom"
+      >
+        <span [ngStyle]="style">
+          <ng-template [ngIf]="isNative">{{ unified }}</ng-template>
+          <ng-content></ng-content>
+        </span>
       </span>
-    </span>
+    </ng-template>
   `,
   changeDetection: ChangeDetectionStrategy.OnPush,
   preserveWhitespaces: false,
 })
-export class EmojiComponent implements OnChanges, Emoji {
+export class EmojiComponent implements OnChanges, Emoji, OnDestroy {
   @Input() skin: Emoji['skin'] = 1;
   @Input() set: Emoji['set'] = 'apple';
   @Input() sheetSize: Emoji['sheetSize'] = 64;
@@ -91,7 +100,14 @@ export class EmojiComponent implements OnChanges, Emoji {
   @Input() sheetColumns?: number;
   @Input() useButton?: boolean;
   @Output() emojiOver: Emoji['emojiOver'] = new EventEmitter();
+  /**
+   * Note: `emojiLeave` and `emojiLeaveOutsideAngular` are dispatched on the same event, but for different
+   *       purposes. The `emojiLeaveOutsideAngular` would be set up in category component so we don't care
+   *       about zone context the callback is being called in. The `emojiLeave` is for backwards compatibility
+   *       if anyone is listening to this event explicitly in their code.
+   */
   @Output() emojiLeave: Emoji['emojiLeave'] = new EventEmitter();
+  @Output() emojiLeaveOutsideAngular: Emoji['emojiLeave'] = new EventEmitter();
   @Output() emojiClick: Emoji['emojiClick'] = new EventEmitter();
   style: any;
   title?: string = undefined;
@@ -103,7 +119,28 @@ export class EmojiComponent implements OnChanges, Emoji {
   @Input() backgroundImageFn: Emoji['backgroundImageFn'] = DEFAULT_BACKGROUNDFN;
   @Input() imageUrlFn?: Emoji['imageUrlFn'];
 
-  constructor(private emojiService: EmojiService) {}
+  @ViewChild('button', { static: false })
+  set button(button: ElementRef<HTMLElement> | undefined) {
+    // Note: `runOutsideAngular` is used to trigger `addEventListener` outside of the Angular zone
+    //       too. See `setupMouseEnterListener`. The `switchMap` will subscribe to `fromEvent` considering
+    //       the context where the factory is called in.
+    this.ngZone.runOutsideAngular(() => this.button$.next(button?.nativeElement));
+  }
+
+  /**
+   * The subject used to emit whenever view queries are run and `button` or `span` is set/removed.
+   * We use subject to keep the reactive behavior so we don't have to add and remove event listeners manually.
+   */
+  private readonly button$ = new Subject<HTMLElement | undefined>();
+
+  private readonly destroy$ = new Subject<void>();
+
+  private readonly ngZone = inject(NgZone);
+  private readonly emojiService = inject(EmojiService);
+
+  constructor() {
+    this.setupMouseLeaveListener();
+  }
 
   ngOnChanges() {
     if (!this.emoji) {
@@ -184,6 +221,10 @@ export class EmojiComponent implements OnChanges, Emoji {
     return (this.isVisible = true);
   }
 
+  ngOnDestroy(): void {
+    this.destroy$.next();
+  }
+
   getData() {
     return this.emojiService.getData(this.emoji, this.skin, this.set);
   }
@@ -202,8 +243,22 @@ export class EmojiComponent implements OnChanges, Emoji {
     this.emojiOver.emit({ emoji, $event });
   }
 
-  handleLeave($event: Event) {
-    const emoji = this.getSanitizedData();
-    this.emojiLeave.emit({ emoji, $event });
+  private setupMouseLeaveListener(): void {
+    this.button$
+      .pipe(
+        // Note: `EMPTY` is used to remove event listener once the DOM node is removed.
+        switchMap(button => (button ? fromEvent(button, 'mouseleave') : EMPTY)),
+        takeUntil(this.destroy$),
+      )
+      .subscribe($event => {
+        const emoji = this.getSanitizedData();
+        this.emojiLeaveOutsideAngular.emit({ emoji, $event });
+        // Note: this is done for backwards compatibility. We run change detection if developers
+        //       are listening to `emojiLeave` in their code. For instance:
+        //       `<ngx-emoji (emojiLeave)="..."></ngx-emoji>`.
+        if (this.emojiLeave.observed) {
+          this.ngZone.run(() => this.emojiLeave.emit({ emoji, $event }));
+        }
+      });
   }
 }

src/lib/picker/picker.component.html

@@ -52,7 +52,7 @@
       [emojiImageUrlFn]="imageUrlFn"
       [emojiUseButton]="useButton"
       (emojiOver)="handleEmojiOver($event)"
-      (emojiLeave)="handleEmojiLeave()"
+      (emojiLeaveOutsideAngular)="handleEmojiLeave()"
       (emojiClick)="handleEmojiClick($event)"
     ></emoji-category>
   </section>