title: Angular 4, difference between httpClient and HttpClientModule
body: <p>In this article <a href="https://medium.com/@amcdnl/the-new-http-client-in-angular-4-3-754bd3ff83a8" rel="noreferrer">here</a> and others :It looks like you need to import HttpClientModule in app.module.ts and HttpClient in app.component.ts  to make a http request. Why? How do they work?</p>