Custom error classes in Node.js - Mini Project: Build & Apply

Custom Error Classes in Node.js

📖 Scenario: You are building a simple Node.js application that processes user input. To handle errors clearly, you want to create a custom error class that extends the built-in Error class.

🎯 Goal: Create a custom error class called ValidationError that extends Error. Then use it to throw an error with a specific message.

📋 What You'll Learn

Create a class named ValidationError that extends Error

Add a constructor that accepts a message parameter

Call the parent Error constructor with the message

Set the name property of the error to ValidationError

Throw an instance of ValidationError with the message 'Invalid input'

💡 Why This Matters

🌍 Real World

Custom error classes help make error handling clearer and more specific in Node.js applications, improving debugging and user feedback.

💼 Career

Understanding custom errors is important for backend developers to write robust, maintainable code and handle different error cases properly.

1

Create the custom error class skeleton

Create a class called ValidationError that extends Error. Add a constructor that takes a message parameter.

Node.js

class ValidationError extends Error {
  // Your code here
}

Need a hint?

Remember to use extends to inherit from Error and call super(message) inside the constructor.

2

Set the error name property

Inside the ValidationError constructor, set this.name to the string 'ValidationError'.

Node.js

class ValidationError extends Error {
  constructor(message) {
    super(message);
    // Your code here
  }
}

Need a hint?

Setting this.name helps identify the error type when caught.

3

Throw the custom error

Write a line that throws a new ValidationError with the message 'Invalid input'.

Node.js

class ValidationError extends Error {
  constructor(message) {
    super(message);
    this.name = 'ValidationError';
  }
}

// Your code here

Need a hint?

Use the throw keyword followed by new ValidationError('Invalid input').

4

Wrap throw in try-catch and log error name and message

Wrap the throw statement inside a try block. Add a catch block that catches the error as err and logs err.name and err.message.

Node.js

class ValidationError extends Error {
  constructor(message) {
    super(message);
    this.name = 'ValidationError';
  }
}

// Your code here

Need a hint?

Use try { ... } catch (err) { ... } and inside catch log the error's name and message.