Function scheduler

packages/reactivity/__tests__/watch.spec.ts:21–28

(job, isFirstRun)

  fn ? resolvedPromise.then(fn) : resolvedPromise

const scheduler: WatchScheduler = (job, isFirstRun) => {
  if (isFirstRun) {
    job()
  } else {
    queue.push(job)
    flushJobs()
  }
}

const flushJobs = () => {
  if (isFlushPending) return