Function apply

packages/reactivity/src/arrayInstrumentations.ts:270–306

(
  self: unknown[],
  method: ArrayMethods,
  fn: (item: unknown, index: number, array: unknown[]) => unknown,
  thisArg?: unknown,
  wrappedRetFn?: (result: any) => unknown,
  args?: IArguments,
)

// instrument functions that read (potentially) all items
// to take ARRAY_ITERATE dependency
function apply(
  self: unknown[],
  method: ArrayMethods,
  fn: (item: unknown, index: number, array: unknown[]) => unknown,
  thisArg?: unknown,
  wrappedRetFn?: (result: any) => unknown,
  args?: IArguments,
) {
  const arr = shallowReadArray(self)
  const needsWrap = arr !== self && !isShallow(self)
  // @ts-expect-error our code is limited to es2016 but user code is not
  const methodFn = arr[method]

  // #11759
  // If the method being called is from a user-extended Array, the arguments will be unknown
  // (unknown order and unknown parameter types). In this case, we skip the shallowReadArray
  // handling and directly call apply with self.
  if (methodFn !== arrayProto[method as any]) {
    const result = methodFn.apply(self, args)
    return needsWrap ? toReactive(result) : result
  }

  let wrappedFn = fn
  if (arr !== self) {
    if (needsWrap) {
      wrappedFn = function (this: unknown, item, index) {
        return fn.call(this, toWrapped(self, item), index, self)
      }
    } else if (fn.length > 2) {
      wrappedFn = function (this: unknown, item, index) {
        return fn.call(this, item, index, self)
      }
    }
  }
  const result = methodFn.call(arr, wrappedFn, thisArg)
  return needsWrap && wrappedRetFn ? wrappedRetFn(result) : result
}

// instrument reduce and reduceRight to take ARRAY_ITERATE dependency
function reduce(