Joi as validation alternative in Express - Mini Project: Build & Apply

Joi as validation alternative

📖 Scenario: You are building a simple Express server that accepts user data through a POST request. Instead of manually checking each field, you want to use Joi to validate the incoming data easily and clearly.

🎯 Goal: Create an Express route that uses Joi to validate a user object with name and age fields before processing it.

📋 What You'll Learn

Create a Joi schema for user data with name as a required string and age as a required number

Create an Express POST route /user that validates the request body using the Joi schema

Send a 400 response with the validation error message if validation fails

Send a 200 response with a success message if validation passes

💡 Why This Matters

🌍 Real World

Validating user input is essential in web apps to avoid errors and security issues. Joi makes this easy and clear.

💼 Career

Backend developers often use Joi or similar libraries to ensure data integrity and improve code readability in APIs.

1

Set up Express app and import Joi

Write code to import express and joi, create an Express app with express(), and add middleware to parse JSON bodies using express.json().

Express

const express = require('express');
const Joi = require('joi');

const app = express();

// Add JSON body parsing middleware
// Your code here

Need a hint?

Use require to import both express and joi. Then create the app with express(). Finally, add app.use(express.json()) to parse JSON request bodies.

2

Create Joi schema for user data

Create a Joi schema called userSchema that requires a name string and an age number.

Express

const express = require('express');
const Joi = require('joi');

const app = express();

app.use(express.json());

// Create Joi schema called userSchema
// Your code here

Need a hint?

Use Joi.object() to create a schema. Inside, define name as Joi.string().required() and age as Joi.number().required().

3

Add POST /user route with Joi validation

Add a POST route /user that validates req.body against userSchema using userSchema.validate(req.body). If there is an error, respond with status 400 and the error message. Otherwise, respond with status 200 and a success message.

Express

const express = require('express');
const Joi = require('joi');

const app = express();

app.use(express.json());

const userSchema = Joi.object({
  name: Joi.string().required(),
  age: Joi.number().required()
});

// Add POST /user route with Joi validation
// Your code here

Need a hint?

Use app.post('/user', (req, res) => { ... }). Inside, validate with userSchema.validate(req.body). If error exists, send 400 with the message. Otherwise, send 200 with success.

4

Start the Express server

Add code to start the Express server on port 3000 using app.listen(3000) and log a message 'Server running on port 3000'.

Express

const express = require('express');
const Joi = require('joi');

const app = express();

app.use(express.json());

const userSchema = Joi.object({
  name: Joi.string().required(),
  age: Joi.number().required()
});

app.post('/user', (req, res) => {
  const { error } = userSchema.validate(req.body);
  if (error) {
    return res.status(400).send(error.details[0].message);
  }
  res.status(200).send('User data is valid');
});

// Start server on port 3000
// Your code here

Need a hint?

Use app.listen(3000, () => { console.log('Server running on port 3000') }) to start the server and show a message.