Express app
- Node.js course
- Intermediate
- Lesson 66/116
- 6 min
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.
Practice 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.
Starter code
const books = [];
books.push({ id: 1, title: "Node.js" });
const express = require("express");
const app = express();
// GET "/" route — send { status: "ok" } JSON response
// write here
// Self-request (boilerplate)
const server = app.listen(3000, () => {
const http = require("http");
http.get("http://localhost:3000/", (res) => {
let body = "";
res.on("data", (c) => body += c);
res.on("end", () => { console.log(body); server.close(); });
});
});Sample solution
app.get("/", (req, res) => {
res.json({ status: "ok" });
});Expected output
{"status":"ok"}
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Complete the GET route
app.____("/", (req, res) => { res.json({ status: "ok" }); });app.get("/", (req, res) => { res.json({ status: "ok" }); });Explanation: app.get defines a GET route.
2 Match each piece to its role
| Term | Meaning |
|---|---|
express |
Web framework |
app.get |
Defines a GET route |
res.json |
Sends a JSON response |
app.listen |
Starts the server |
3 Which HTTP method does app.get handle in Express?
app.get("/", handler)- POST
- GET Correct answer
- DELETE
- PUT
Explanation: app.get handles only GET requests.