Centralized error handling in Node.js - Mini Project: Build & Apply

Centralized Error Handling in Node.js

📖 Scenario: You are building a simple Node.js server that responds to client requests. To keep your code clean and easy to maintain, you want to handle all errors in one place instead of repeating error handling in every route.

🎯 Goal: Create a Node.js server using Express that has centralized error handling. You will set up a route that can cause an error, then create an error handler middleware to catch and respond to errors in a friendly way.

📋 What You'll Learn

Create an Express app with one route /error that throws an error

Add a variable PORT set to 3000

Use a try-catch block or next() to pass errors to the error handler

Create an error handling middleware function with four parameters: err, req, res, next

Send a JSON response with status and message from the error handler

Start the server listening on PORT

💡 Why This Matters

🌍 Real World

Centralized error handling helps keep server code clean and consistent. It makes debugging easier and improves user experience by sending clear error messages.

💼 Career

Most Node.js backend jobs require knowledge of Express and error handling to build reliable APIs and web servers.

1

Set up Express app and route

Create a variable express by requiring 'express'. Then create a variable app by calling express(). Finally, create a route /error on app that throws a new Error with the message 'Something went wrong!'.

Node.js

const express = require('express');
const app = express();

// Create /error route that throws an error
// Your code here

Need a hint?

Use require('express') to import Express. Then call express() to create the app. Use app.get('/error', ...) to create the route that throws an error.

2

Add PORT variable

Create a constant variable called PORT and set it to 3000.

Node.js

const express = require('express');
const app = express();

app.get('/error', (req, res, next) => {
    throw new Error('Something went wrong!');
});

// Create PORT variable set to 3000
// Your code here

Need a hint?

Use const PORT = 3000; to create the port variable.

3

Create centralized error handler middleware

Add an error handling middleware function to app with four parameters: err, req, res, next. Inside it, send a JSON response with status set to 500 and message set to err.message.

Node.js

const express = require('express');
const app = express();

app.get('/error', (req, res, next) => {
    throw new Error('Something went wrong!');
});

const PORT = 3000;

// Add error handling middleware below
// Your code here

Need a hint?

Use app.use with four parameters to create error middleware. Use res.status(500).json(...) to send the error response.

4

Start the server listening on PORT

Call app.listen with PORT and a callback function that does nothing (empty arrow function).

Node.js

const express = require('express');
const app = express();

app.get('/error', (req, res, next) => {
    throw new Error('Something went wrong!');
});

const PORT = 3000;

app.use((err, req, res, next) => {
    res.status(500).json({ status: 500, message: err.message });
});

// Start server listening on PORT
// Your code here

Need a hint?

Use app.listen(PORT, () => {}) to start the server.