import { Component, OnInit } from '@angular/core';

import { AuthenticationService } from '../authentication.service';

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

credentials: {
    username: '',
    password: ''
};

constructor(private _authenticationService: AuthenticationService) {}

ngOnInit() { }

login() {

    this._authenticationService.login(this.credentials).subscribe(
        response => console.log(response),
        error => console.log(error),
        () => console.log('Done.')
    );

}

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

@Injectable()
export class AuthenticationService {

constructor() { }

login(credentials) {

    console.log(credentials); // This is undefined

}