Error Handling

Proper error handling makes your code robust and debuggable.

Try-Catch-Finally

try {
  // Code that might throw an error
  const data = JSON.parse(invalidJson);
} catch (error) {
  // Handle the error
  console.error('Parse error:', error.message);
} finally {
  // Always runs
  console.log('Cleanup complete');
}

Throwing Errors

function divide(a, b) {
  if (b === 0) {
    throw new Error('Division by zero');
  }
  return a / b;
}
// Custom error types
class ValidationError extends Error {
  constructor(message) {
    super(message);
    this.name = 'ValidationError';
  }
}
throw new ValidationError('Email is invalid');

Error Types

// Built-in error types
new Error('Generic error');
new TypeError('Type mismatch');
new ReferenceError('Variable not found');
new SyntaxError('Invalid syntax');
new RangeError('Value out of range');
// Checking error type
try {
  // ...
} catch (error) {
  if (error instanceof TypeError) {
    console.log('Type error occurred');
  } else if (error instanceof ReferenceError) {
    console.log('Reference error occurred');
  }
}

Async Error Handling

// With promises
fetchData()
  .then(data => process(data))
  .catch(error => console.error(error));
// With async/await
async function getData() {
  try {
    const data = await fetchData();
    return data;
  } catch (error) {
    console.error('Failed to fetch:', error);
    throw error; // Re-throw if needed
  }
}

Best Practices

// 1. Be specific about what you catch
try {
  // Specific operation
} catch (error) {
  if (error.code === 'NETWORK_ERROR') {
    // Handle network error
  } else {
    throw error; // Re-throw unexpected errors
  }
}
// 2. Log errors with context
function processUser(userId) {
  try {
    // Process
  } catch (error) {
    console.error(Error processing user ${userId}:, error);
    throw error;
  }
}
// 3. Use error boundaries in React
class ErrorBoundary extends React.Component {
  componentDidCatch(error, info) {
    logError(error, info);
  }
}