# Proper Error Handling

Handle errors gracefully and provide meaningful error messages.

## Provide Context

```javascript
// Bad - Vague error
throw new Error("Failed");

// Good - Specific context
throw new Error(`Failed to fetch user with ID ${userId}: User not found`);
```

## Use Try-Catch Appropriately

```javascript
// Bad - Silent failure
try {
  await saveData(data);
} catch (error) {
  // Nothing - error is lost
}

// Good - Handle or propagate
try {
  await saveData(data);
} catch (error) {
  logger.error('Failed to save data:', error);
  throw new DataSaveError('Could not save user data', { cause: error });
}
```

## Create Custom Error Classes

```javascript
class ValidationError extends Error {
  constructor(field, message) {
    super(`Validation failed for ${field}: ${message}`);
    this.name = 'ValidationError';
    this.field = field;
  }
}

class NotFoundError extends Error {
  constructor(resource, id) {
    super(`${resource} with ID ${id} not found`);
    this.name = 'NotFoundError';
    this.statusCode = 404;
  }
}
```

## Fail Fast

```javascript
// Good - Validate early
function processUser(user) {
  if (!user) {
    throw new ValidationError('user', 'User is required');
  }
  if (!user.email) {
    throw new ValidationError('email', 'Email is required');
  }
  
  // Process with confidence
  sendWelcomeEmail(user.email);
}
```

## Don't Catch Everything

```javascript
// Bad - Too broad
try {
  await complexOperation();
} catch (error) {
  return null; // Hides all errors
}

// Good - Catch specific errors
try {
  await complexOperation();
} catch (error) {
  if (error instanceof NetworkError) {
    return retryWithBackoff();
  }
  throw error; // Propagate unexpected errors
}
```

## User-Friendly Messages

```javascript
// Bad - Technical error for users
alert("Uncaught TypeError: Cannot read property 'name' of undefined");

// Good - User-friendly message
alert("We couldn't load your profile. Please refresh the page.");
// Log technical details separately for debugging
logger.error(error);
```