login.component.ts

import { Component, OnInit } from '@angular/core'
import { AuthService } from '../services/auth.service'
import { Router } from '@angular/router'

@Component({
  selector: 'app-login',
  templateUrl: './login.component.html',
  styleUrls: ['./login.component.css']
})
export class LoginComponent implements OnInit {
  isInvalid: boolean = false

  constructor(
    private authService: AuthService,
    private router: Router) { }

  ngOnInit() {
  }

  submit(f) {
    const credentials = f.value

    this.authService.login(credentials)
      .subscribe(result => {
        this.router.navigate([''])
      },
      error => {
        if (error === 'Unauthorized.') {
          this.isInvalid = true
        }
      })
  }
}