Microtask Queue
Promise callbacks (.then, .catch, async continuations) run in the microtask queue — before the next macrotask (setTimeout, setInterval) but after the current synchronous code.
JavaScript
Advanced
5 min read
Microtasks and Event Loop
Example
console.log("1 sync");
setTimeout(() => console.log("3 macrotask"), 0);
Promise.resolve().then(() => console.log("2 microtask"));
console.log("1b sync");
// Output: "1 sync", "1b sync", "2 microtask", "3 macrotask" Pro Tip
Microtasks flush completely before any macrotask runs — starving with microtasks blocks rendering.
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