Function markRef

packages/react-reconciler/src/ReactFiberBeginWork.js:1382–1401

(current: Fiber | null, workInProgress: Fiber)

}

function markRef(current: Fiber | null, workInProgress: Fiber) {
  // TODO: Check props.ref instead of fiber.ref when enableRefAsProp is on.
  const ref = workInProgress.ref;
  if (ref === null) {
    if (current !== null && current.ref !== null) {
      // Schedule a Ref effect
      workInProgress.flags |= Ref | RefStatic;
    }
  } else {
    if (typeof ref !== 'function' && typeof ref !== 'object') {
      throw new Error(
        'Expected ref to be a function, an object returned by React.createRef(), or undefined/null.',
      );
    }
    if (current === null || current.ref !== ref) {
      // Schedule a Ref effect
      workInProgress.flags |= Ref | RefStatic;
    }
  }
}

function mountIncompleteFunctionComponent(
  _current: null | Fiber,