Function onWatcherCleanup

packages/reactivity/src/watch.ts:103–118

(
  cleanupFn: () => void,
  failSilently = false,
  owner: ReactiveEffect | undefined = activeWatcher,
)

 * By default, the current active effect.
 */
export function onWatcherCleanup(
  cleanupFn: () => void,
  failSilently = false,
  owner: ReactiveEffect | undefined = activeWatcher,
): void {
  if (owner) {
    let cleanups = cleanupMap.get(owner)
    if (!cleanups) cleanupMap.set(owner, (cleanups = []))
    cleanups.push(cleanupFn)
  } else if (__DEV__ && !failSilently) {
    warn(
      `onWatcherCleanup() was called when there was no active watcher` +
        ` to associate with.`,
    )
  }
}

export function watch(
  source: WatchSource | WatchSource[] | WatchEffect | object,