Express app

Set up the API skeleton with an Express app.

The Express app

The second lesson sets up the Express app. Express is the most popular web framework for Node.js. You create an app with const express = require("express"); const app = express();.

To define a route you use app.get(path, handler). For example app.get("/", (req, res) => res.json({ status: "ok" })) sends a JSON response to the root path. req is the request and res is the response. res.json() turns an object into JSON and sends the response. To start the server you call app.listen(port, cb). In this lesson we add the root route and verify the API is alive.

Responding with res.json

res.json(data) turns data into a JSON string and sends the response. The content type is automatically application/json. This is the most common response method in APIs.

For example res.json({ status: "ok" }) produces the response {"status":"ok"}. You could use res.send() too, but for JSON res.json is better because it handles the content type and serialization automatically. In this lesson the GET / route returns { status: "ok" } so we can see the API is alive. In later lessons we return real data with a /books route.

Exercise Define the root route

Define a GET "/" route. The handler should return the object { status: "ok" } as JSON with res.json. The self-request part is already in the starting code.

Show example solution

app.get("/", (req, res) => {
  res.json({ status: "ok" });
});

Test yourself

Complete the GET route

app.____("/", (req, res) => { res.json({ status: "ok" }); });

Show answer

app.get("/", (req, res) => { res.json({ status: "ok" }); });

Match each piece to its role

express

Web framework
app.get

Defines a GET route
res.json

Sends a JSON response
app.listen

Starts the server
Which HTTP method does app.get handle in Express?
```
app.get("/", handler)
```
- POST
- GET
- DELETE
- PUT
Show answer

GET — app.get handles only GET requests.

Next lesson: CRUD routes

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