forwardRef

export default function forwardRef<Props, ElementType: React$ElementType>(
  render: (props: Props, ref: React$Ref<ElementType>) => React$Node,
) {
  // 开发环境校验报错
  if (__DEV__) {
    // 如果封装的不是函数，则抛出错误
    if (typeof render !== 'function') {
      warningWithoutStack(
        false,
        'forwardRef requires a render function but was given %s.',
        render === null ? 'null' : typeof render,
      );
    } else {
      // 如果对应组件的入参只有一个或者超出两个则抛出错误，正常 forwardRef 的组件应该有两个入参 （props, ref）
      warningWithoutStack(
        // Do not warn for 0 arguments because it could be due to usage of the 'arguments' object
        // 如果没有入参可能是内部使用了 arguments 来获取入参，所以不抛出错误
        render.length === 0 || render.length === 2,
        'forwardRef render functions accept exactly two parameters: props and ref. %s',
        render.length === 1
          ? 'Did you forget to use the ref parameter?'
          : 'Any additional parameter will be undefined.',
      );
    }
    if (render != null) {
         // 由于 forwardRef 不支持类组件所以如果发现对应情况，则抛出错误
      warningWithoutStack(
        render.defaultProps == null && render.propTypes == null,
        'forwardRef render functions do not support propTypes or defaultProps. ' +
          'Did you accidentally pass a React component?',
      );
    }
  }
  // 返回一个 React Forward Ref Type 类型的 React 元素
  return {
    $$typeof: REACT_FORWARD_REF_TYPE,
    render,
  };
}