Node.js — Error Handling

Try-Catch

try {
    const data = JSON.parse(invalidJson);
} catch (error) {
    console.error('Parse error:', error.message);
}

Error Types

Type	Description
Error	Base error class
TypeError	Wrong type
ReferenceError	Undefined variable
SyntaxError	Invalid syntax
RangeError	Out of range

Custom Errors

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

throw new ValidationError('Invalid email', 'email');

Error Handling Patterns

// Callback
function fetchData(callback) {
    fs.readFile('data.json', (err, data) => {
        if (err) return callback(err);
        callback(null, JSON.parse(data));
    });
}

// Promise
function fetchData() {
    return fs.promises.readFile('data.json')
        .then(data => JSON.parse(data));
}

// Async/Await
async function fetchData() {
    try {
        const data = await fs.promises.readFile('data.json');
        return JSON.parse(data);
    } catch (error) {
        console.error('Error:', error.message);
        throw error;
    }
}

Uncaught Exceptions

process.on('uncaughtException', (error) => {
    console.error('Uncaught Exception:', error);
    process.exit(1);
});

process.on('unhandledRejection', (reason) => {
    console.error('Unhandled Rejection:', reason);
});

Mini Practice

1. Use try-catch
2. Create custom error classes
3. Handle async errors
4. Add global error handlers

Up Next

Continue with Debugging — debugging Node.js applications.