Interview Q&A / Node.js

31. Should you use await inside a for loop or Promise.all for independent tasks?

    For independent tasks use Promise.all with map so they run concurrently. await inside a loop runs them one by one, which is right only when each step depends on the last or order and rate limits matter.

    IntermediateQuick answer1 min read
32. What are the main phases of the Node.js event loop?

    Timers, pending callbacks, idle/prepare, poll, check, and close callbacks. Timers run setTimeout callbacks, poll collects I/O, check runs setImmediate, and microtasks are drained between steps.

    IntermediateQuick answer1 min read
33. What is a circular dependency in Node.js and what happens when it occurs?

    A circular dependency is when module A requires B and B requires A. In CommonJS, the second module receives A's partially filled exports at that moment, so values defined later are undefined. Fix it by restructuring.

    IntermediateQuick answer1 min read
34. What is backpressure in Node.js streams?

    Backpressure is when a writable cannot consume data as fast as a readable produces it. The writable signals this, and the reader should pause, otherwise memory fills up with unwritten data.

    IntermediateQuick answer1 min read
35. What is the difference between stream.pipe and stream.pipeline?

    pipe connects streams but does not forward errors or clean up, so a failure can leave streams open. pipeline connects several streams, destroys all of them on error, and reports the result in one callback or promise.

    IntermediateQuick answer1 min read
36. What is top-level await and where can you use it in Node.js?

    It lets you use await directly at the top of a file without wrapping it in an async function. It works only in ES modules, and it delays anything that imports that module until the promise settles.

    IntermediateQuick answer1 min read
37. Write a Transform stream that converts incoming text to uppercase.

    Extend stream.Transform (or pass a transform function), call this.push with the changed chunk, and call the callback when done. Then pipe a readable into it and into a writable.

    IntermediateQuick answerCoding1 min read