Function iterator

packages/reactivity/src/arrayInstrumentations.ts:233–261

(
  self: unknown[],
  method: keyof Array<unknown>,
  wrapValue: (value: any) => unknown,
)

// instrument iterators to take ARRAY_ITERATE dependency
function iterator(
  self: unknown[],
  method: keyof Array<unknown>,
  wrapValue: (value: any) => unknown,
) {
  // note that taking ARRAY_ITERATE dependency here is not strictly equivalent
  // to calling iterate on the proxied array.
  // creating the iterator does not access any array property:
  // it is only when .next() is called that length and indexes are accessed.
  // pushed to the extreme, an iterator could be created in one effect scope,
  // partially iterated in another, then iterated more in yet another.
  // given that JS iterator can only be read once, this doesn't seem like
  // a plausible use-case, so this tracking simplification seems ok.
  const arr = shallowReadArray(self)
  const iter = (arr[method] as any)() as IterableIterator<unknown> & {
    _next: IterableIterator<unknown>['next']
  }
  if (arr !== self && !isShallow(self)) {
    iter._next = iter.next
    iter.next = () => {
      const result = iter._next()
      if (!result.done) {
        result.value = wrapValue(result.value)
      }
      return result
    }
  }
  return iter
}

// in the codebase we enforce es2016, but user code may run in environments
// higher than that