MEAN Node.js Async Patterns and Performance 4

Question 1

What does the `util.promisify()` function do in Node.js?

Accepted Answer

Converts a callback-based function to return a Promise

Answer

`util.promisify()` takes a function following the Node.js error-first callback convention and returns a version that returns Promises.

Question 2

Which Node.js method limits the concurrency of multiple async operations?

Accepted Answer

There is no built-in method; use a semaphore pattern

Answer

Node.js has no built-in concurrency limiter; developers implement semaphore/queue patterns or use libraries like `p-limit` to cap parallel operations.

Question 3

What is the output order of this code: `console.log('A'); setTimeout(() => console.log('B'), 0); Promise.resolve().then(() => console.log('C')); console.log('D');`

Accepted Answer

A, D, C, B

Answer

Synchronous code (A, D) runs first, then microtasks like Promise callbacks (C), then macrotasks like setTimeout (B).

Question 4

What is `AsyncLocalStorage` used for in Node.js?

Accepted Answer

Storing request-scoped context across async operations without passing it explicitly

Answer

`AsyncLocalStorage` provides a way to store data that is accessible throughout the lifetime of a web request or any other asynchronous duration.

Question 5

What happens when an unhandled rejection occurs in a Promise in Node.js v15+?

Accepted Answer

The process exits with a non-zero exit code

Answer

Since Node.js v15, unhandled Promise rejections cause the process to terminate with exit code 1 by default.

MEAN - Stack Development Practice Test

MEAN - Stack Development Practice Test

MEAN Node.js Async Patterns and Performance 4