Express Middleware

Express Middleware

Middleware là functions xử lý requests trong pipeline.

Built-in Middleware

import express from "express";

const app = express();

app.use(express.json()); // Parse JSON
app.use(express.urlencoded({ extended: true })); // Parse form data
app.use(express.static("public")); // Serve static files

Custom Middleware

// Logger middleware
function logger(req, res, next) {
  console.log(`${req.method} ${req.url}`);
  next();
}

app.use(logger);

Authentication Middleware

function authMiddleware(req, res, next) {
  const token = req.headers.authorization?.split(" ")[1];

  if (!token) {
    return res.status(401).json({ error: "No token provided" });
  }

  try {
    const decoded = jwt.verify(token, process.env.JWT_SECRET);
    req.user = decoded;
    next();
  } catch (error) {
    res.status(401).json({ error: "Invalid token" });
  }
}

// Protected route
app.get("/profile", authMiddleware, (req, res) => {
  res.json({ user: req.user });
});

Error Handler

function errorHandler(err, req, res, next) {
  console.error(err);

  if (err.name === "ValidationError") {
    return res.status(400).json({ error: err.message });
  }

  res.status(500).json({ error: "Internal server error" });
}

app.use(errorHandler);