unwatch

// user watcher 收集 dep 是为了 unwatch
Vue.prototype.$watch = function (
  expOrFn: string | (() => any),
  cb: any,
  options?: Record<string, any>
): Function {
  return function unwatchFn() {
    watcher.teardown()
  }
}

teardown() {
  let i = this.deps.length
  while (i--) {
    this.deps[i].removeSub(this)
  }
}