MEAN Node.js Async Patterns and Performance

Question 1

What is the Node.js Event Loop and why is it important for MEAN stack applications?

Accepted Answer

A single-threaded mechanism that processes async callbacks without blocking, enabling high concurrency

Answer

A loop that processes DOM events in the browser

Answer

A queue that manages database transactions sequentially

Answer

A multi-threaded scheduler for parallel task execution

Question 2

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

Accepted Answer

nextTick() fires before I/O callbacks in the current iteration; setImmediate() fires after I/O callbacks in the next iteration

Answer

nextTick() fires after I/O callbacks; setImmediate() fires before I/O callbacks

Answer

Both fire at the same time but nextTick() has higher priority for CPU tasks

Answer

nextTick() is synchronous; setImmediate() is asynchronous

Question 3

What are Node.js Worker Threads used for?

Accepted Answer

Running CPU-intensive JavaScript in parallel on separate threads without blocking the event loop

Answer

Managing worker processes in a PM2 cluster

Answer

Handling database connection pooling

Answer

Processing web socket connections concurrently

Question 4

What does `Promise.all()` do in Node.js async programming?

Accepted Answer

Runs multiple Promises in parallel and resolves when all complete or rejects when any fails

Answer

Runs Promises sequentially and collects all results

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Retries failed Promises automatically until all succeed

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Cancels all Promises if one fails

Question 5

What is Node.js clustering and how does it relate to a MEAN stack API server?

Accepted Answer

Creates multiple worker processes that share the same server port to utilize all CPU cores

Answer

Groups Node.js instances behind a load balancer on different ports

Answer

Clusters database connections for better performance

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Creates redundant server instances for failover

Question 6

What is a memory leak in Node.js and what is a common cause in Express applications?

Accepted Answer

When objects are kept in memory indefinitely, commonly caused by event listeners that are never removed

Answer

When the heap exceeds 1.5GB and crashes the process

Answer

When garbage collection pauses the event loop for too long

Answer

When stream buffers aren't flushed after responding