Node.js Async Patterns & Error Handling 4

Question 1

What is the difference between `process.nextTick()` and `setImmediate()` in Node.js?

Accepted Answer

`process.nextTick()` fires at the end of the current operation before I/O; `setImmediate()` fires in the check phase after I/O

Answer

`process.nextTick()` callbacks run before any I/O or timers after the current operation, while `setImmediate()` runs in the check phase after I/O events.

Question 2

What does `util.callbackify()` do in Node.js?

Accepted Answer

Converts an async/Promise-returning function into a Node.js callback-style function

Answer

`util.callbackify()` takes an async function and returns a function that calls a Node.js-style (err, result) callback instead of returning a promise.

Question 3

Which pattern allows you to avoid uncaught errors when using `async` functions as Express route handlers?

Accepted Answer

Wrap the handler in try/catch and call next(err) on error

Answer

Express does not catch async errors automatically, so you must wrap with try/catch and pass errors to `next(err)` to trigger error-handling middleware.

Question 4

What is 'backpressure' in Node.js streams?

Accepted Answer

The mechanism where a writable stream signals a readable stream to slow down data production

Answer

Backpressure occurs when a writable stream's buffer is full; it signals upstream readable streams to pause so the system doesn't run out of memory.

Question 5

What is a common pitfall when using `async` functions inside `Array.prototype.forEach()`?

Accepted Answer

Errors thrown inside the async callback are silently lost and forEach doesn't await the callbacks

Answer

`forEach` ignores returned promises, so async callbacks run without being awaited, and any rejections become unhandled promise rejections.

Node.js Practice Test

Node.js Practice Test

Node.js Async Patterns & Error Handling 4