angular-cn/public/docs/_examples/router/ts/app/auth.guard.ts

// #docregion
import { Injectable }          from '@angular/core';
import { CanActivate, Router } from '@angular/router';
import { AuthService }         from './auth.service';

@Injectable()
export class AuthGuard implements CanActivate {
  constructor(private authService: AuthService, private router: Router) {}

  canActivate() {
    if (this.authService.isLoggedIn) { return true; }
    this.router.navigate(['/login']);
    return false;
  }
}