Hello, future full-stack developer! Let's learn server-side programming. Today, we're going to focus on routes and middlewares in Express.js. Our goal is to help you design efficient servers that can process complex web requests. We'll apply the lessons we learned to a full-stack application using React for our client. Let's get started!

Think of routes in Express.js as routes on a map, each of which directs an HTTP request. They're defined by a URL pattern and an HTTP method (GET, POST). Express.js uses these routes to process client requests.

Path parameters are variables in the routes, while query parameters add extra data to the URL. Let's look at how to log information about stars.

For example, endpoint /api/star/:id has a path parameter of id, we can query this endpoint with an URL like /api/star/123. In contrast, query parameters are added after the URL path by adding a question mark (?) and then adding the query parameters. For example: /api/stars?type=sun has a query parameter of type with the value sun.

Let’s fetch data for our React client using Axios. We'll retrieve a star's data.

In this snippet, Axios sends a GET request to fetch data about a star with a specified ID from our server, then logs the response data.

In this piece of code, we request and log details about Sun stars from our server.

Middlewares in Express.js control how your server processes requests and responses, similar to traffic controllers. Middlewares are like functions that are applied to your requests, before these requests actually get executed. For example, let’s create a middleware that logs the time of each request (before the request is actually executed):

Next, let's create another middleware that logs the request method.

The middlewares are executed in the order they are defined.

Middlewares and routes are like the yin and yang of an Express.js server - they complete each other. Together, they define how the server handles and responds to client requests.

We now have an Express.js server that uses a chain of middlewares and routes to process client requests. Our middlewares log each request's timing and type, and the appropriate routes then process these requests.

Congratulations! We've learned about routes and middlewares in Express.js, which means we can now create servers that can manage a variety of client requests.

Try out our practice exercises that are coming up next. Then, join us for our next space voyage, where we'll explore RESTful APIs and error handling in Express.js. Until then, happy coding!