Express Basics

Express

npm install express\n\nconst express = require("express");\nconst app = express();\n\napp.use(express.json());       // parse JSON bodies\n\napp.get("/", (req, res) => {\n  res.json({ message: "API is running" });\n});\n\napp.listen(3000, () => console.log("Listening on 3000"));

Routes

app.get("/courses", getAllCourses);\napp.get("/courses/:id", getOneCourse);\napp.post("/courses", createCourse);\napp.put("/courses/:id", updateCourse);\napp.delete("/courses/:id", deleteCourse);

The request object

app.get("/courses/:id", (req, res) => {\n  console.log(req.params.id);   // /courses/12 → 12\n  console.log(req.query.page);  // ?page=2\n  console.log(req.body);        // parsed JSON body\n  console.log(req.headers);\n});

The response object

res.json({ ok: true });\nres.status(201).json({ id: 1 });\nres.status(404).json({ error: "Not found" });\nres.redirect("/");\nres.sendFile("./file.pdf", { root: __dirname });

Project structure

server.js            # entry, app setup\nroutes/\n├─ courses.js\n└─ users.js\ncontrollers/\n├─ courseController.js\nservices/  models/  middleware/\nconfig/  .env  package.json

Tip: req.params are from the URL path, req.query from ? args, req.body from the submitted JSON. Keep the three straight.