Sample Login Service

login.service.ts

import { Injectable } from '@angular/core';

@Injectable()
export class LoginService {

  constructor() { }

  testUser = {username: 'tester', password: 'password'};
  loggedIn = false;

  isLoggedIn() {
    return this.loggedIn;
  }

  login(username, password) {
     if (username === this.testUser.username && password === this.testUser.password) {
       this.loggedIn = true;
     }
     return this.isLoggedIn();
  }
}