Why understanding req matters in Express

Introduction

Understanding req helps you get information from the user's request. This lets your app respond correctly.

When you want to read data sent by a user in a form.

When you need to check what URL or path the user asked for.

When you want to get details like cookies or headers from the user's browser.

When you want to handle different types of requests like GET or POST.

When you want to read query parameters from the URL.

Syntax

Express

app.get('/path', (req, res) => {
  // use req to get info
  const data = req.body;
  const query = req.query;
  const params = req.params;
  // respond
  res.send('Got your data');
});

req stands for request and holds all info sent by the user.

You use req.body for form data, req.query for URL queries, and req.params for URL parts.

Examples

Get a user ID from the URL part and send it back.

Express

app.get('/user/:id', (req, res) => {
  const userId = req.params.id;
  res.send(`User ID is ${userId}`);
});

Read a search term from the URL query and respond with it.

Express

app.get('/search', (req, res) => {
  const term = req.query.term;
  res.send(`Search term is ${term}`);
});

Read form data sent by POST and greet the user.

Express

app.post('/submit', (req, res) => {
  const name = req.body.name;
  res.send(`Hello, ${name}`);
});

Sample Program

This program starts a server that listens for POST requests at /greet. It reads the name from the request body and replies with a greeting. If no name is sent, it says Hello, Guest!

Express

import express from 'express';
const app = express();
app.use(express.json());

app.post('/greet', (req, res) => {
  const name = req.body.name || 'Guest';
  res.send(`Hello, ${name}!`);
});

app.listen(3000, () => {
  console.log('Server running on http://localhost:3000');
});

Important Notes

Always use middleware like express.json() to read JSON data from req.body.

Check if the data exists in req before using it to avoid errors.

Understanding req helps you make your app respond to what users send.

Summary

req holds all info sent by the user to your server.

You use req.params, req.query, and req.body to get different parts of the request.

Knowing how to use req helps your app understand and respond to users correctly.