Async and the Event Loop

async / await and Promises work out of the box. The built-in helper delay(ms, value) returns a Promise that resolves to value after ms milliseconds — handy for examples and tests:

async function main() {
  let v = await delay(10, "timer done")
  console.log(v)
}
main()

text

Promise { <pending> }     ← top-level echo: the return value of the main() call
timer done                ← after the timer fires, the await resumes

The timer family:

API	Description
`setTimeout(fn, ms)`	Runs after a delay, returns a timer id; `clearTimeout(id)` cancels it
`setInterval(fn, ms)`	Runs repeatedly; `clearInterval(id)` cancels it
`setStrictTimeout` and friends	Strict timer variants with controllable precision, for time-sensitive scenarios
`requestIdleCallback(fn)`	Idle-time callback; does not block the critical path
`delay(ms, value?)`	Gox helper: resolves to the given value after a delay

Exit semantics

The script does not exit immediately while timers or async callbacks are still pending — the event loop drives them all to completion. That is why the main() above manages to print its result.

Async and the Event Loop ​

Async and the Event Loop