Node.js Async Patterns & Error Handling 5

Question 1

What is the correct error-first callback convention in Node.js?

Accepted Answer

callback(error, result)

Answer

Node.js convention requires callbacks to receive the error as the first argument (null if none) and the result as the second.

Question 2

Which of the following creates a Promise that resolves after a given delay?

Accepted Answer

new Promise(resolve => setTimeout(resolve, ms))

Answer

`new Promise(resolve => setTimeout(resolve, ms))` uses the built-in `setTimeout` to delay resolution — there is no native `Promise.delay()`.

Question 3

What happens when you call `next(err)` in Express.js middleware?

Accepted Answer

Control passes to the next error-handling middleware (a function with 4 parameters)

Answer

Passing any truthy value to `next()` skips remaining regular middleware and routes, forwarding to the nearest error-handling middleware (defined with `(err, req, res, next)`).

Question 4

What is the behavior of `Promise.all()` when one of its promises rejects?

Accepted Answer

It immediately rejects with the error from the first rejected promise

Answer

`Promise.all()` short-circuits on the first rejection: the returned promise immediately rejects with that error, even if other promises are still pending.

Question 5

Which async iteration construct should you use to consume a Node.js Readable stream line by line in modern Node.js?

Accepted Answer

for await...of with the stream

Answer

Node.js streams implement the async iterator protocol, so `for await...of stream` is the idiomatic way to consume them asynchronously without callbacks.

Node.js Practice Test

Node.js Practice Test

Node.js Async Patterns & Error Handling 5