创建 ref

一个具有单个可变值的不变对象

// an immutable object with a single mutable value
// 一个具有单个可变值的不变对象
export function createRef(): RefObject {
  const refObject = {
    current: null,
  };
  if (__DEV__) {
    Object.seal(refObject); // 封锁当前对象
  }
  return refObject;
}