Lesson 24 — watchEffect

Effects that track themselves

watchEffect(fn) runs fn immediately and records every reactive value fn reads. Whenever any of them changes, it runs fn again. Unlike watch, you do not list the sources — Vue discovers them automatically.

watchEffect(() => {
  document.title = cartCount.value + " items" // re-runs when cartCount changes
})

Why it matters: syncing to the page title, localStorage or a log stays correct without listing dependencies by hand.