Questions
3 of 15
1Explain the event loop.
2Explain process.next.tick()
3What could be the disadvantages of process.nextTick()
4Why use process.nextTick()?
5What is the difference between the microtask queue and the macrotask (callback) queue?
6How does Promise.then() differ from setTimeout() in terms of execution order?
7What is queueMicrotask()? How does it differ from Promise.resolve().then()?
8How does the event loop handle long-running synchronous code? What is 'blocking the event loop' and how do you avoid it in production?
9How would you profile and detect event loop lag in a production Node.js service? What tools and metrics do you use? (e.g., perf_hooks, Clinic.js, event_loop_utilization)
10How does the browser's event loop differ from Node.js's event loop?
11How do streams and backpressure in Node.js relate to the event loop? Why does improper stream handling block or overload the loop?
12What is 'starvation' in the context of the event loop? Give a real-world example.
13How do you design a CPU-intensive task (e.g., image processing, ML inference) in a Node.js app without blocking the event loop?
14How does the event loop relate to memory leaks? Can retained closures in the callback queue prevent garbage collection?
15What strategies do you use to keep the event loop healthy at scale? (offloading, chunking, job queues like BullMQ, worker threads)
nodejsnodejs
Basics
Event Loop
Buffers
Streams
Events
Time functions
Clusters
Crypto
Modules
Worker Threads
File Operations
Threads
Performance Optimisation
Websockets
03 / 15

What could be the disadvantages of process.nextTick()

This can 'starve' your I/O by making a recursive process.nextTick() calls, which prevents the event loop from reaching the poll phase.

setImmediate() vs setTimeout(): setImmediate() and setTimeout() are similar, but behave in different ways depending on when they are called.
  1. 1

    setImmediate() is designed to execute a script once the current poll phase is completed.

  2. 2

    setTimeout() schedules a script to be run after a minimum threshold in ms has elapsed. The order in which the timers are executed will vary depending on the context in which they are called. If both are called from within the main module, then the timing will be bound by the performance of the process (which can be impacted by other applications running on the machine).

  3. 3

    The main advantage to using setImmediate() over setTimeout() is setImmediate() will always be executed before any timers if scheduled within an I/O cycle, independently of how many timers are present.

Difficulty: 5/10
Topics: event loop, microtask queue, starvation

Scenario Questions

0-2 years experience
  1. 1

    If you use process.nextTick inside a tight loop, what will happen to the rest of the event loop?

  2. 2

    How would you decide whether to use process.nextTick versus setImmediate for a callback that must run after the current function finishes?

  3. 3

    What could go wrong if you schedule a large number of nextTick callbacks before any I/O events?

2-5 years experience
  1. 1

    You notice that a request handler is becoming slower after adding a few process.nextTick calls. Walk me through how you would debug the performance issue.

  2. 2

    Explain why using process.nextTick for deferring work in a high‑traffic API could cause request latency spikes.

  3. 3

    A teammate replaced setTimeout(...,0) with process.nextTick and the server started crashing under load. What likely caused the crash?

5-8 years experience
  1. 1

    Design a strategy to prevent event‑loop starvation when a library you depend on uses process.nextTick extensively.

  2. 2

    How would you refactor a module that currently uses process.nextTick for async flow to be more resilient at scale?

  3. 3

    Discuss the trade‑offs of using process.nextTick versus promises in a microservice that must handle thousands of concurrent connections.

8+ years experience
  1. 1

    At a large organization, several services rely on process.nextTick for internal task scheduling. What architectural guidelines would you establish to mitigate long‑term maintenance and performance risks?

  2. 2

    If you were planning a migration away from process.nextTick across multiple teams, how would you coordinate the change and ensure backward compatibility?

  3. 3

    Consider a scenario where a critical library uses process.nextTick for error propagation. How would you evaluate the impact of replacing it with async/await across the platform?

Follow-up Questions

  • ❓Can you walk me through a concrete example where this problem showed up?
  • ❓What metrics would you monitor to detect nextTick‑related starvation?
  • ❓How would you test that your mitigation actually resolves the issue?