Your First HTTP Server

Introduction

A web server listens for requests and sends back responses. Node includes everything you need to build one, with no packages. Understanding this foundation makes frameworks such as Express much easier to understand.

The simplest server

What each part does:

• createServer takes a function that runs for every request.
• req describes the request: req.method (such as GET) and req.url (the path).
• res is how you answer: writeHead sets the status code and headers, and end sends the body and finishes the response.
• server.listen(3000) starts listening on port 3000. Open http://localhost:3000/hello in a browser.

Always send a response for every path, or the visitor waits forever.

Testing it from code

Node includes the fetch function, the same one browsers have. Here is a complete script that starts the server on any free port (port 0), calls it and stops. The outputs come from a real run:

200 { message: 'Hello' }
404 { error: 'Not found' }

Using port 0 asks the operating system for a free port, which is handy in tests.

Status codes and headers

• 200 OK, 201 Created, 204 No Content
• 400 Bad Request (the client sent something wrong), 404 Not Found
• 500 Internal Server Error (something broke on your side)

Set the content-type header so clients know how to read the body, such as application/json or text/html.

Reading a request body

The body arrives in pieces, so you collect them:

Then parse it with JSON.parse, inside a try block, because clients can send invalid JSON. Limit the size of bodies you accept, so one huge request cannot use all your memory.

Why use a framework?

Handling routes with if statements, parsing bodies, validation, errors and security headers by hand gets repetitive. Frameworks such as Express handle the routine parts. You will use Express in the intermediate course, and you will understand what it does for you.

Staying safe

• Never send raw error details or stack traces to users in production.
• Validate everything that comes from a request.
• Do not serve files from user-supplied paths without strict checks.
• Do not expose a development server to the internet.

Try it yourself

Add a /time route that returns the current time as JSON, and a /echo route that returns the query string you send. Test both with fetch.

Summary

• createServer runs your function for each request, and you answer with a status, headers and a body.
• Return JSON with the right status codes, and always respond for unknown paths.
• Test servers with fetch, and use a framework when routing and validation grow.