Manual validation patterns in Express - Mini Project: Build & Apply

Manual validation patterns in Express

📖 Scenario: You are building a simple Express server that accepts user registration data. You want to manually check the data before saving it.

🎯 Goal: Create an Express route that manually validates the username and age fields from the request body. If validation passes, respond with success; otherwise, respond with an error message.

📋 What You'll Learn

Create an Express app with a POST route at /register

Manually check that username exists and is a string

Manually check that age exists and is a number greater than or equal to 18

Send a JSON response with { success: true } if valid

Send a JSON response with { success: false, error: 'message' } if invalid

💡 Why This Matters

🌍 Real World

Manual validation is common in backend servers to ensure data is correct before processing or saving.

💼 Career

Backend developers often write manual validation logic in Express to handle user input safely and provide clear error messages.

1

Set up Express app and import modules

Write code to import express, create an app with express(), and use express.json() middleware.

Express

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

Need a hint?

Use require('express') to import Express. Create the app by calling express(). Use app.use(express.json()) to parse JSON bodies.

2

Create POST route at /register

Add a POST route handler on app for path '/register' with parameters req and res.

Express

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

// Your code here

Need a hint?

Use app.post('/register', (req, res) => { ... }) to create the route.

3

Manually validate username and age

Inside the /register route, extract username and age from req.body. Check if username is a string and exists, and age is a number >= 18. If invalid, respond with res.json({ success: false, error: 'Invalid input' }) and return.

Express

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

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

Need a hint?

Use const { username, age } = req.body to get data. Check types with typeof. Use return res.json(...) to send error and stop.

4

Send success response and start server

If validation passes, respond with res.json({ success: true }). 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('/register', (req, res) => {
  const { username, age } = req.body;
  if (typeof username !== 'string' || !username) {
    return res.json({ success: false, error: 'Invalid input' });
  }
  if (typeof age !== 'number' || age < 18) {
    return res.json({ success: false, error: 'Invalid input' });
  }
  // Your code here
});

// Your code here

Need a hint?

Send success with res.json({ success: true }). Start server with app.listen(3000).