isReadonly

setup() {
  // 检查对象是否是由 readonly 创建的只读代理。
  const original = reactive({ count: 123 });
  console.log(isReadonly(original), 'original'); // false

  const originalCopy = readonly(original);
  console.log(isReadonly(originalCopy), 'originalCopy'); // true

  const copy = readonly({ count: 1 });
  console.log(isReadonly(copy), 'copy'); // true
}