Node.js Async Patterns & Error Handling 3

Question 1

What does the `unhandledRejection` event on `process` allow you to do?

Accepted Answer

Catch promise rejections that have no `.catch()` handler attached

Answer

The `process.on('unhandledRejection', handler)` event fires when a Promise is rejected and no rejection handler is attached within the current event loop turn.

Question 2

What does `async function foo() { return 42; }` return when called?

Accepted Answer

A Promise that resolves to 42

Answer

All async functions implicitly wrap their return value in `Promise.resolve()`, so calling an async function always returns a Promise.

Question 3

Which of the following correctly handles an error thrown inside a Promise executor?

Accepted Answer

The Promise automatically rejects; attach a .catch() handler

Answer

Any exception thrown synchronously inside a Promise executor is automatically converted to a promise rejection.

Question 4

What is the difference between `Promise.race()` and `Promise.any()`?

Accepted Answer

`Promise.race()` resolves/rejects with the first settled promise; `Promise.any()` resolves with the first fulfilled promise

Answer

`Promise.race()` settles (resolve or reject) as soon as the first promise settles, while `Promise.any()` ignores rejections and resolves with the first fulfillment.

Question 5

In Node.js streams, what event should you listen to for handling stream errors?

Accepted Answer

'error'

Answer

All Node.js streams inherit from EventEmitter and emit an 'error' event when something goes wrong; unhandled stream errors crash the process.

Node.js Practice Test

Node.js Practice Test

Node.js Async Patterns & Error Handling 3