目标

实现两个小工具函数，来判断是否为 响应性 对象和 只读对象

it('isReactive', () => {
  const original = { foo: 1 };
  const observed = reactive(original); 
  expect(isReactive(observed)).toBe(true);
  expect(isReactive(original)).toBe(false);
});
it('happy path', () => { 
  const original = { foo: 1, bar: { baz: 2 } };
  const wrapped = readonly(original); 
  expect(isReadonly(wrapped)).toBe(true);
  expect(isReadonly(original)).toBe(false);
});

实现

因为在 baseHandlers 的 createGetter 中是有 isReadonly 的入参，所以只要想办法触发 get 就能知道是不是 reactive / readonly

export enum ReactiveFlags {
  IS_REACTIVE = '__v_isReactive',
  IS_READONLY = '__v_isReadonly',
}
export function isReactive(value) {
  return !!value[ReactiveFlags.IS_REACTIVE];
}
export function isReadonly(value) {
  return !!value[ReactiveFlags.IS_READONLY];
}

import { ReactiveFlags } from './reactive';
function createGetter(isReadonly = false) {
  return function get(target, key) { 
    if (key === ReactiveFlags.IS_REACTIVE) {
      return !isReadonly;
    } else if (key === ReactiveFlags.IS_READONLY) {
      return isReadonly;
    }
    const res = Reflect.get(target, key);
    if (!isReadonly) {
      track(target, key);
    }
    return res;
  };
}