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 be refactoring 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 multi-tier application stack.

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 be using the HTTP client object to do so. The general pattern for an Express request handler in this case is as follows:

exports.index = function(req, res) {
    callAsyncOrRESTservice...