Validating body fields in Express - Mini Project: Build & Apply

Validating body fields

📖 Scenario: You are building a simple Express server that accepts user data through a POST request. To keep your server safe and reliable, you need to check that the user sends the right information in the request body.

🎯 Goal: Create an Express server that validates the name and email fields in the request body before processing the data.

📋 What You'll Learn

Create an Express app

Add middleware to parse JSON request bodies

Check that the name field exists and is a string

Check that the email field exists and contains an '@' symbol

Send a 400 error response if validation fails

Send a 200 success response if validation passes

💡 Why This Matters

🌍 Real World

Validating user input on the server helps prevent errors and security issues in web applications.

💼 Career

Backend developers often write validation logic to ensure data integrity and improve user experience.

1

Set up Express app and JSON parser

Create a variable called express that requires the 'express' module. Then create a variable called app by calling express(). Finally, add the JSON body parser middleware by calling app.use(express.json()).

Express

const express = require('express');
const app = express();
// Your code here

Need a hint?

Use require('express') to import Express. Then call express() to create the app. Use app.use(express.json()) to parse JSON bodies.

2

Create POST route with validation variables

Add a POST route handler on /submit using app.post. Inside the handler function, create two variables: name and email, which get their values from req.body.name and req.body.email respectively.

Express

const express = require('express');
const app = express();
app.use(express.json());

app.post('/submit', (req, res) => {
  // Your code here
});

Need a hint?

Use app.post('/submit', (req, res) => { ... }) to create the route. Inside, get name and email from req.body.

3

Add validation logic for name and email

Inside the POST handler, add an if statement that checks if name is not a string or is missing, or if email is not a string or does not include '@'. If any check fails, respond with status 400 and JSON { error: 'Invalid input' }.

Express

const express = require('express');
const app = express();
app.use(express.json());

app.post('/submit', (req, res) => {
  const name = req.body.name;
  const email = req.body.email;
  // Your code here
});

Need a hint?

Check if name is missing or not a string, or if email is missing, not a string, or missing '@'. Use res.status(400).json(...) to send error.

4

Send success response for valid input

After the validation if block, send a JSON response with status 200 and message { message: 'Data received' }. Then add app.listen(3000) to start the server on port 3000.

Express

const express = require('express');
const app = express();
app.use(express.json());

app.post('/submit', (req, res) => {
  const name = req.body.name;
  const email = req.body.email;
  if (typeof name !== 'string' || !name || typeof email !== 'string' || !email.includes('@')) {
    return res.status(400).json({ error: 'Invalid input' });
  }
  // Your code here
});

// Your code here

Need a hint?

Send success JSON with res.status(200).json({ message: 'Data received' }). Start server with app.listen(3000).