How do you handle errors in Express.js and send meaningful responses to the client?

Question

ICSM Computer · Answer

Error handling in Express.js is essential for building reliable and user-friendly APIs. Express provides a built-in way to handle errors gracefully and send meaningful responses to the client.
Basics of Error Handling in Express.js
and 
1. Use Express's Error-Handling Middleware
Express error-handling middleware is defined by a function with four arguments:
(err, req, res, next).
app.use((err, req, res, next) =andgt; {
  console.error(err.stack); // log the error for debugging
  res.status(err.status || 500).json({
    success: false,
    message: err.message || 'Internal Server Error',
  });
});
and 
2. Throwing Errors in Routes or Controllers
app.get('/api/user/:id', async (req, res, next) =andgt; {
  try {
    const user = await User.findById(req.params.id);
    if (!user) {
      const error = new Error('User not found');
      error.status = 404;
      throw error;
    }
    res.json({ success: true, data: user });
  } catch (err) {
    next(err); // Pass the error to the error-handling middleware
  }
});
and 
Create a Reusable Error Class (Optional but Recommended)
and 
// utils/ApiError.js
class ApiError extends Error {
  constructor(status, message) {
    super(message);
    this.status = status;
  }
}
module.exports = ApiError;
Use it like this:
const ApiError = require('./utils/ApiError');
if (!user) {
  throw new ApiError(404, 'User not found');
}
and 
Catch Async Errors with a Wrapper
// utils/catchAsync.js
module.exports = fn =andgt; (req, res, next) =andgt; {
  Promise.resolve(fn(req, res, next)).catch(next);
};
// Usage
app.get('/api/test', catchAsync(async (req, res) =andgt; {
  throw new Error('Something went wrong!');
}));
and 
Tips for Better Error Handling
Tip
Description
Custom Status Codes
Use appropriate HTTP status codes (e.g., 400, 401, 403, 404, 500).
Consistent Format
Send consistent error response shape: { success: false, message, code, etc. }
Validation Errors
Use middleware like express-validator and return validation-specific errors.
Hide Stack in Production
Avoid sending error stacks to clients in production environments.
Catch Async Errors
Wrap async functions or use a wrapper like express-async-handler.
and

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How do you handle errors in Express.js and send meaningful responses to the client?

ICSM Computer

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1 Answers

Basics of Error Handling in Express.js

1. Use Express's Error-Handling Middleware

2. Throwing Errors in Routes or Controllers

Create a Reusable Error Class (Optional but Recommended)

Catch Async Errors with a Wrapper

Tips for Better Error Handling

Liked By

Tip	Description
Custom Status Codes	Use appropriate HTTP status codes (e.g., 400, 401, 403, 404, 500).
Consistent Format	Send consistent error response shape: `{ success: false, message, code, etc. }`
Validation Errors	Use middleware like `express-validator` and return validation-specific errors.
Hide Stack in Production	Avoid sending error stacks to clients in production environments.
Catch Async Errors	Wrap async functions or use a wrapper like `express-async-handler`.