Node.js: How does the event loop handle microtasks vs macrotasks in Node.js?

Microtasks (Promise callbacks, queueMicrotask) run after each macrotask. Macrotasks (setTimeout, I/O) run one per loop iteration.

Execution order:

• 1. Run all microtasks.
• 1. Run one macrotask.
• 1. Repeat.

1setTimeout(() => console.log("macrotask 1"), 0);
2setTimeout(() => console.log("macrotask 2"), 0);
3Promise.resolve().then(() => console.log("microtask 1"));
4Promise.resolve().then(() => console.log("microtask 2"));
5// Output: microtask 1, microtask 2, macrotask 1, macrotask 2

Key points:

• Microtasks have higher priority.
• All microtasks drain before the next macrotask.
• process.nextTick is even higher priority than Promises.