Express JS Express Error Handling

Question 1

How many parameters must an Express error-handling middleware function declare?

Accepted Answer

4 (err, req, res, next)

Answer

Express identifies error-handling middleware by its four-parameter signature: err, req, res, and next.

Question 2

How do you pass a custom error to the Express error handler from a route?

Accepted Answer

next(new Error('message'))

Answer

Calling next() with an Error object routes the error to the next error-handling middleware.

Question 3

What is the default HTTP status code Express sends if an error reaches the error handler without res.status() being set?

Accepted Answer

500

Answer

Express uses a 500 Internal Server Error status by default when an error reaches the error handler without an explicit status code.

Question 4

Which approach correctly handles errors in Express async route handlers?

Accepted Answer

Wrap in try/catch and call next(err)

Answer

Async errors must be caught with try/catch and forwarded via next(err), or wrapped with an async error handler utility.

Question 5

What does passing a string to next() (e.g., next('Something went wrong')) do in Express?

Accepted Answer

Triggers the error-handling middleware with that string as the error

Answer

Passing any truthy value (including a string) to next() bypasses normal middleware and jumps to error handlers.

Express JS Practice Test