Warn user of unsaved changes before leaving page

***Component:

import { ComponentCanDeactivate } from './pending-changes.guard';
import { HostListener } from '@angular/core';
import { Observable } from 'rxjs/Observable';

export class MyComponent implements ComponentCanDeactivate {
  // @HostListener allows us to also guard against browser refresh, close, etc.
  @HostListener('window:beforeunload')
  canDeactivate(): Observable<boolean> | boolean {
    // insert logic to check if there are pending changes here;
    // returning true will navigate without confirmation
    // returning false will show a confirm dialog before navigating away
  }
}

***Guard.ts

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

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

@Injectable()
export class PendingChangesGuard implements CanDeactivate<ComponentCanDeactivate> {
  canDeactivate(component: ComponentCanDeactivate): boolean | Observable<boolean> {
    // if there are no pending changes, just allow deactivation; else confirm first
    return component.canDeactivate() ?
      true :
      // NOTE: this warning message will only be shown when navigating elsewhere within your angular app;
      // when navigating away from your angular app, the browser will show a generic warning message
      // see http://stackoverflow.com/a/42207299/7307355
      confirm('WARNING: You have unsaved changes. Press Cancel to go back and save these changes, or OK to lose these changes.');
  }
}

***Route:

import { PendingChangesGuard } from './pending-changes.guard';
import { MyComponent } from './my.component';
import { Routes } from '@angular/router';

export const MY_ROUTES: Routes = [
  { path: '', component: MyComponent, canDeactivate: [PendingChangesGuard] },
];

***Module:

import { PendingChangesGuard } from './pending-changes.guard';
import { NgModule } from '@angular/core';

@NgModule({
  // ...
  providers: [PendingChangesGuard],
  // ...
})
export class AppModule {}