This Angular 7 class and decorator can be used to perform component cleanup actions when a user logs out.

logout-cleanup-component.ts

import {OnDestroy, OnInit} from '@angular/core';
import {AuthService} from '../service/auth/auth.service';
import {Subscription} from 'rxjs';


/**
 * To use this class and the decorator below (must be used together):
 *
 * @CleanupAfterLogout()
 * @Component({
 *   selector: '...',
 *   templateUrl: '...'
 * })
 * export class MyComponentThatHoldsSensitiveData extends LogoutCleanupComponent {
 *   ...
 *   onLogout(): void {
 *      console.log('Perform my logout actions');
 *   }
 *   ...
 * }
 */
export abstract class LogoutCleanupComponent implements OnDestroy, OnInit {
  // noinspection JSMethodCanBeStatic
  private get componentSuperclass() {
    return 'LogoutCleanupComponent';
  }

  private isLoggedInSubscription: Subscription;

  protected constructor(private auth: AuthService) {
  }

  abstract onLogout(): void;

  private superOnInit(): void {
    this.isLoggedInSubscription = this.auth.isLoggedIn.subscribe(
      isLoggedIn => {
        if (!isLoggedIn) {
          this.onLogout();
          this.isLoggedInSubscription.unsubscribe();
        }
      },
      console.error);
  }

  private superOnDestroy(): void {
    // Give the logout page time to trigger logout (if the user is navigating to the logout page)
    setTimeout(() => {
      this.isLoggedInSubscription.unsubscribe();
    }, 250);
  }

  ngOnInit(): void {
  }

  ngOnDestroy(): void {
  }
}


/**
 * To use this decorator and the class above (must be used together):
 *
 * @CleanupAfterLogout()
 * @Component({
 *   selector: '...',
 *   templateUrl: '...'
 * })
 * export class MyComponentThatHoldsSensitiveData extends LogoutCleanupComponent {
 *   ...
 *   onLogout(): void {
 *      console.log('Perform my logout actions');
 *   }
 *   ...
 * }
 */
export function CleanupAfterLogout(): ClassDecorator {
  return (constructor: any) => {
    if (constructor.prototype.componentSuperclass !== 'LogoutCleanupComponent') {
      throw new Error('CleanupAfterLogout() decorator only applies to classes extending LogoutCleanupComponent!');
    }

    const originalNgOnInit = constructor.prototype.ngOnInit;
    const originalNgOnDestroy = constructor.prototype.ngOnDestroy;

    constructor.prototype.ngOnInit = function() {
      constructor.prototype.superOnInit.apply(this);
      // tslint:disable-next-line:no-unused-expression
      originalNgOnInit && typeof originalNgOnInit === 'function' && originalNgOnInit.apply(this);
    };

    constructor.prototype.ngOnDestroy = function() {
      constructor.prototype.superOnDestroy.apply(this);
      // tslint:disable-next-line:no-unused-expression
      originalNgOnDestroy && typeof originalNgOnDestroy === 'function' && originalNgOnDestroy.apply(this);
    };
  };
}