Explain the difference between a flowing and a non-flowing readable stream.

0-2 years experience

1. 1If you create a readable file stream and immediately attach a 'data' listener, what mode does the stream operate in and why?
2. 2You need to read a small config file line by line without loading the whole file into memory. Which stream mode would you choose and how would you control the flow?
3. 3What happens if you call stream.read() on a readable stream that hasn't been switched to flowing mode?

2-5 years experience

1. 1Your service processes incoming HTTP request bodies using a readable stream, but it stalls when the client sends data slowly. How would you check whether the stream is flowing or paused, and what would you change?
2. 2During a migration a teammate replaced a 'data' event listener with async iteration, and now you see 'readable' event errors. Explain why the original flow mode mattered and how to fix it.
3. 3You have a transform stream that buffers data until a certain size before pushing downstream. How does backpressure interact with flowing vs non‑flowing mode, and what would you adjust to avoid memory bloat?

5-8 years experience

1. 1Design a high‑throughput log ingestion pipeline that reads many files concurrently. How do you decide when to keep streams flowing versus paused, and what mechanisms enforce backpressure across the pipeline?
2. 2A production bug shows a readable stream's internal buffer growing unbounded under load, causing OOM. Walk through how the choice of flow mode could cause this and propose a robust fix.
3. 3When integrating a third‑party library that expects a paused readable stream, but your code currently pipes a flowing stream into it, what steps would you take to reconcile the mismatch without rewriting the library?

8+ years experience

1. 1Your organization is moving from event‑driven flowing streams to async‑iterator pipelines for better composability. What architectural considerations, migration path, and cross‑team guidelines would you establish regarding stream flow modes?
2. 2Explain the long‑term trade‑offs of enforcing a policy that all new Node.js services must use non‑flowing streams with explicit backpressure handling, especially for performance, developer ergonomics, and observability.
3. 3In a multi‑tenant SaaS platform, you need to guarantee isolation of streaming resources. How would you design a stream manager that can dynamically switch streams between flowing and paused states based on tenant quotas and system load?