Now that we've seen how to make HTTP client requests, we can look at how to make a REST query inside an Express web application. What that effectively means is to make an HTTP GET request to a backend server, which responds with the Fibonacci number represented by the URL. To do so, we'll refactor the Fibonacci application to make a Fibonacci server that is called from the application. While this is overkill for calculating Fibonacci numbers, it lets us look at the basics of implementing a multitier application stack in Express.
Inherently, calling a REST service is an asynchronous operation. That means calling the REST service will involve a function call to initiate the request and a callback function to receive the response. REST services are accessed over HTTP, so we'll use the HTTP client object to do so.