Error Handling in Koa.js: Best Practices

Error handling is a crucial aspect of building robust Node.js applications with Koa.js. Today, I’ll share some battle-tested practices I’ve learned while working with Koa’s error handling mechanisms.

Understanding Koa’s Error Handling Flow

Koa’s error handling is elegantly simple yet powerful. It leverages async/await and middleware patterns to catch and process errors effectively. Let’s dive into the key concepts.

Global Error Handler

One of the first things I always set up in my Koa applications is a global error handler. Here’s how I structure it:

app.use(async (ctx, next) => {
  try {
    await next();
  } catch (err) {
    ctx.status = err.status || 500;
    ctx.body = {
      success: false,
      message: err.message || 'Internal Server Error'
    };
    ctx.app.emit('error', err, ctx);
  }
});

Custom Error Classes

I’ve found that creating custom error classes helps maintain consistency across the application:

class APIError extends Error {
  constructor(message, status = 400) {
    super(message);
    this.status = status;
    this.name = 'APIError';
  }
}

Error Events and Logging

When things go wrong in production, proper logging becomes invaluable:

app.on('error', (err, ctx) => {
  console.error('Server Error:', {
    message: err.message,
    stack: err.stack,
    path: ctx.request.path,
    method: ctx.request.method
  });
});

Validation Error Handling

Always validate input data and handle validation errors gracefully:

const validateUser = async (ctx, next) => {
  const { email, password } = ctx.request.body;
  if (!email || !password) {
    throw new APIError('Missing required fields', 400);
  }
  await next();
};

Best Practices Summary

• Always use try/catch blocks in middleware
• Implement custom error classes for different scenarios
• Set up comprehensive error logging
• Use middleware for validation
• Keep error responses consistent
• Handle both sync and async errors
• Don’t expose sensitive error details in production

Remember, good error handling isn’t just about catching errors – it’s about providing meaningful feedback and maintaining application stability.