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Custom Handlers

In the previous exercise, we used the express.static middleware, which serves static files using a built-in handler.

An HTTP handler in Express is typically a function with the following signature:

(req: Request, res: Response) => Promise<void>;

To handle an incoming HTTP request, all a handler function requires is the request object and a response object in order to communicate back to the client.

Assignment

Let's add a readiness endpoint to the Chirpy server! Readiness endpoints are used by external systems to check if our server is ready to receive traffic.

The endpoint should be accessible at the /healthz path.

The endpoint should simply return a 200 OK status code indicating that it has started up successfully and is listening for traffic. The endpoint should return a Content-Type: text/plain; charset=utf-8 header, and the body will contain a message that simply says "OK" (the text associated with the 200 status code).

1. Add the Readiness Endpoint

Create src/api/readiness.ts and export a handlerReadiness function from it. In src/index.ts, import it from "./api/readiness.js". You can also keep the handler in src/index.ts.

The Express app object has methods matching the HTTP methods. The parameters are the path and the handler function. In src/index.ts, use the .get method to add a handler for the /healthz path.

Import the Express types explicitly: import { Request, Response } from "express";
These are Express's Request/Response objects, which differ from the Fetch API's Response

app.get("/healthz", handlerReadiness);

Your handler should use various methods of the response object to do the following:

Set the Content-Type header using .set
Send the body text using .send

Express automatically sets the status code to 200. If you want to change it, you can use the .status method.

2. Update the Static Files Path

Now that we've added a new handler, we don't want potential conflicts with the static files handler. Update the static file serving to use the /app/ path instead of /.

To do this:

Use the express.static middleware alongside app.use to mount the /app path, making sure the request paths get handled correctly.
create a new src/app directory and move the index.html file there.
Move the assets directory into the src/app directory.

app.use("/app", express.static("./src/app"));

Ensure the server handles requests for both the readiness endpoint and static files correctly.

Run and submit the CLI tests.