angular-cn/aio/content/examples/router/src/app/can-deactivate.guard.ts

// #docregion
import { Injectable }    from '@angular/core';
import { CanDeactivate } from '@angular/router';
import { Observable }    from 'rxjs';

export interface CanComponentDeactivate {
 canDeactivate: () => Observable<boolean> | Promise<boolean> | boolean;
}

@Injectable({
  providedIn: 'root'
})
export class CanDeactivateGuard implements CanDeactivate<CanComponentDeactivate> {
  canDeactivate(component: CanComponentDeactivate) {
    return component.canDeactivate ? component.canDeactivate() : true;
  }
}