Response, Request and Routers

Response

In Express.js, the response object (res) represents the HTTP response that an Express app sends when it receives a request.

Common Response Methods

res.send("Hello, World!");      // Sends plain text/HTML
res.json({ name: "Ronald" });     // Sends JSON response
res.status(404).send("Not Found"); // Sets status code
res.redirect("/home");          // Redirects to another route
res.download("file.pdf");       // Prompts file download
res.end();                      // Ends the response process

• res.send() → Sends text, HTML, or JSON automatically detected
• res.json() → Always sends JSON
• res.status() → Sets HTTP status code
• res.redirect() → Redirects to another URL

Request

The request object (req) contains all information about the HTTP request.

Common Request Properties

app.get("/profile/:id", (req, res) => {
  console.log(req.params.id);     // Route params
  console.log(req.query.name);    // Query string ?name=aman
  console.log(req.body);          // Data from POST/PUT body
  console.log(req.method);        // HTTP method (GET, POST, etc.)
  console.log(req.url);           // URL of the request
  res.send("Profile Page");
});

• req.params → Dynamic route parameters
• req.query → Query string parameters
• req.body → Data sent in the request body (requires middleware like express.json())
• req.method → HTTP method
• req.url → Request URL

Routers

Routers help organize routes into separate files for better structure.

Example of Router

// routes/user.js
const express = require("express");
const router = express.Router();

router.get("/", (req, res) => res.send("User List"));
router.post("/", (req, res) => res.send("Create User"));
router.get("/:id", (req, res) => res.send(`User ${req.params.id}`));

module.exports = router;

Using Router in Main App

// app.js
const express = require("express");
const app = express();
const userRoutes = require("./routes/user");

app.use("/users", userRoutes);

app.listen(3000, () => console.log("Server running on port 3000"));

• Visiting /users/ → "User List"
• Visiting /users/42 → "User 42"
• Visiting /users with POST → "Create User"