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

3 (err, req, res)

Answer

2 (err, next)

Answer

5 (err, req, res, next, app)

Question 2

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

Accepted Answer

next(new Error('message'))

Answer

throw new Error('message')

Answer

res.error(new Error('message'))

Answer

app.error(new Error('message'))

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

404

Answer

400

Answer

503

Question 4

Which approach correctly handles errors in Express async route handlers?

Accepted Answer

Wrap in try/catch and call next(err)

Answer

Use async/await without try/catch

Answer

Use Promise.resolve()

Answer

Express automatically catches async errors

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

Logs the string to console

Answer

Redirects to a route named by that string

Answer

Sends a 400 response

Question 6

In Express, where must error-handling middleware be placed relative to other middleware?

Accepted Answer

At the very end, after all routes and other middleware

Answer

At the beginning, before routes

Answer

Anywhere in the stack

Answer

Inside individual route handlers