1
Returns: A object, with access to stdout and stderr as streams.
2
The result of the spawn function is a child process instance that implements EventEmitterAPI.
3
Suitable for handling large amounts of data because it streams results
4
Gives you fine-grained control over the child process's input/output.
5
Use it when you need to run a command, and you expect real-time output (e.g., streaming logs from a CLI tool).
6
The child_process.spawnSync() function provides equivalent functionality in a synchronous manner that blocks the event loop until the spawned process either exits or is terminated.
7
Handlers for events can be attached or registered to the child instance created.
8
The spawn method is used to create child processes for long-lived, I/O-intensive tasks. It's more efficient than exec for processes that need to stream data.
9
The child_process.spawn() method spawns the child process asynchronously, without blocking the Node.js event loop.

javascript

child.js

Difficulty: 6/10

Topics: child-process, ipc, parallel-processing

0-2 years experience

1
You need to offload a heavy JSON parsing task so the main event loop stays responsive. Walk me through how you'd use fork() to do that — what files you'd create, how you'd pass the data, and how you'd get the result back.
2
A teammate wrote a forked script that logs 'hello' but the parent never receives the message. What are the first three things you'd check in the child and parent code?

2-5 years experience

1
We're processing 10k user uploads per minute. Each upload needs CPU-intensive image validation. You've prototyped with fork() but memory usage grows until the pod OOMs. What's likely leaking, and how would you fix it without rewriting the validator?
2
A forked worker occasionally hangs and never sends its 'done' message. The parent waits forever. How would you add a timeout and cleanup so the parent can retry or mark the job failed?

5-8 years experience

1
Design a fork-based worker pool for a video transcoding service. You need to limit concurrency, handle backpressure when the queue backs up, and ensure zero message loss during deployments. Sketch the parent-child protocol and the scaling strategy.
2
Your team is migrating from fork() to worker_threads for a real-time analytics pipeline. What specific bugs or behavior changes should you watch for during the cutover, and how would you validate parity in production?

8+ years experience

1
The platform team wants to deprecate fork() in favor of a unified job queue (e.g., BullMQ) across all services. You own a legacy service that forks 50+ workers for custom ML inference. Outline a migration plan that avoids downtime, preserves exactly-once semantics, and lets both systems coexist during rollout.
2
A security audit flags that fork() inherits the parent's open file descriptors and env vars, leaking secrets to third-party npm packages running in the child. Propose a defense-in-depth strategy that works across all existing fork usages without rewriting each child script.