CODEWITHSUNDEEP
javascript
ts-alan
ts-alan

Reputation: 99

what works before on eventloop?Microtasks or macrotasks?

I'm investigating the event loop. But I ran into a question. What works before on eventloop? Microtasks or macrotasks? if I run the following code

Promise.resolve().then(()=> console.log('Promise'));
setTimeOut(()=>console.log("setTimeout"),0);

console.log show "Promise setTimeout"; but according to an answer Difference between microtask and macrotask within an event loop context Macrotasks works before microtask.

Upvotes: 1

Views: 92

Answers (1)

Radu Diță
Radu Diță

Reputation: 14191

Macrotasks are processed before other microtasks, but after a macrotask finishes all of the microtasks that are scheduled are going to run. A corollary of this is that 2 macrotasks cannot run one after another if there are some microtasks already scheduled.

Your current JS loop run (where you're running Promise and setTimeout) is actually a Macrotask. Promise schedules a microtask and setTimeout a macrotask.

When the current script ends, a Macrotask ends and the runtime looks into the microtask queue. It resolves the Promise and, if no other microtasks are scheduled from this run it will run the next Macrotask. In your case this is the setTimeout method.

Upvotes: 0

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