watch runs side effects when sources change — useful for async syncing. This lesson covers practical patterns, syntax, and mistakes to avoid.
watch runs side effects when sources change — useful for async syncing.
Prefer computed for pure derived data; watch for effects.
watch(userId, async (id) => {
user.value = await fetchUser(id)
})Fetch when an id changes.
immediate, deep, flushQuick reference for patterns covered in this lesson.
| Item | Example | Purpose |
|---|---|---|
| watch | effect | API |
| watchEffect | auto deps | API |
| immediate | run now | Option |
| deep | nested | Option |
| stop | handle | Cleanup |
| flush | timing | Advanced |
Stop watchers when appropriate; handle races in async callbacks.
Pro Tip
When fetching, watch an explicit id source for clarity.