Location of ngClass definition:

export declare class NgClass implements DoCheck {
    private _iterableDiffers;
    private _keyValueDiffers;
    private _ngEl;
    private _renderer;
    private _iterableDiffer;
    private _keyValueDiffer;
    private _initialClasses;
    private _rawClass;
    constructor(_iterableDiffers: IterableDiffers, _keyValueDiffers: KeyValueDiffers, _ngEl: ElementRef, _renderer: Renderer2);
    set klass(value: string);
    set ngClass(value: string | string[] | Set<string> | {
        [klass: string] :any;
    });
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A practical example:

@Component({
  selector: "app-root".template: ` 
      

        Hello 
      
 `
})
export class AppComponent implements AfterViewInit {
  ngAfterViewInit(): void {
    setTimeout(() = > {
      this.jerry = "changed!";
    }, 0);
  }
  jerry = "Jerry Hello";
  header = true;
}
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Finally, in the _applyIterableChanges function, add a class to the div tag:

More of Jerry’s original articles can be found in “Wang Zixi” :