Overview

To build a web application these days we need to make a number of calls to external HTTP APIs.

Angular comes with its own HTTP client library which we can use to make those calls.

In JavaScript making HTTP requests is an asynchronous operation. It just sends the HTTP request to the API and doesn’t wait for a response before continuing with the next line of code.

When the API responds milliseconds or seconds or minutes later then we get notified and we can start processing the response.

In Angular there are two ways of handling these asynchronous operations. We can use Promises which we covered in the lecture on TypeScript & ES6, or we can use Observables which we covered in the section on RxJS and Observables.

In this chapter you are going to learn: