Error Handling and Validation in Node.js and Express: Building Robust APIs


Building robust APIs not only involves creating features but also ensuring the application can gracefully handle errors and validate incoming data. In this article, we’ll explore error handling techniques and data validation in the context of Node.js and Express. By implementing these practices, you can enhance the reliability and security of your RESTful API.

Handling Errors with Express Middleware:

Global Error Handler:

Implement a global error handler middleware to catch and handle errors at a centralized level. Create a file named errorHandler.js:

// errorHandler.js
const errorHandler = (err, req, res, next) => {

  res.status(500).json({ error: 'Internal Server Error' });

module.exports = errorHandler;

Now, include this middleware in your main app.js file:

// app.js
const express = require('express');
const mongoose = require('mongoose');
const errorHandler = require('./errorHandler');
const app = express();
const PORT = 3000;

// ... (previous code)


app.listen(PORT, () => {
  console.log(`Server is running on http://localhost:${PORT}`);

This middleware will catch any unhandled errors and send a 500 Internal Server Error response.

Custom Error Handling Middleware:

Create custom error handling middleware for specific scenarios. For example, if a resource is not found, return a 404 error:

// app.js
// ... (previous code)

const notFoundHandler = (req, res, next) => {
  res.status(404).json({ error: 'Not Found' });


// ... (rest of the code)

This middleware will be triggered when no route matches the incoming request.

Data Validation with Express-Validator:

To ensure the integrity of incoming data, use a validation library like express-validator. Install it with:

npm install express-validator

Now, integrate it into your app.js file:

// app.js
const express = require('express');
const { body, validationResult } = require('express-validator');
const app = express();
const PORT = 3000;

// ... (previous code)

app.use(express.json());'/register', [
  body('username').isLength({ min: 3 }),
  body('password').isLength({ min: 5 }),
], (req, res) => {
  const errors = validationResult(req);

  if (!errors.isEmpty()) {
    return res.status(400).json({ errors: errors.array() });

  // Rest of the registration logic

  res.status(201).json({ message: 'User registered successfully' });

// ... (rest of the code)

Here, the express-validator checks the length of the username and password and returns a 400 Bad Request response with validation errors if they don’t meet the criteria.


By incorporating global and custom error handling middleware and utilizing data validation techniques, you can fortify your Node.js and Express applications against unexpected issues and ensure the integrity of incoming data. As you continue to develop your APIs, consider exploring more advanced validation techniques, such as schema validation and input sanitization, to further secure your applications. Stay tuned for more articles as we delve deeper into the world of Node.js development. Happy coding!