手写丐版immerjs

手写丐版immerjs：

const createProxy = (target) => {

  const data = {
    __initial: target,
    __copy: null,
    __isModified:false
  }
  
  const handler = {
    get(state, attr) {
      if(!state.__isModified)return state.__initial[attr]
      if (state.__initial[attr] === 'object') {
        if (state.__copy === null) {
          state.__copy = {
            ...state.__initial
          }
        }
        createProxy(state.__initial[attr])
      }
      return state.__copy[attr]
    },
    set(state, attr, value) {
      state.__isModified = true
      state.__copy = {
        ...state.__initial,
        [attr]: value
      }
    }
  }
  
  const {
    proxy
  } =Proxy.revocable(data, handler)
  return proxy
}

const immerjs = (data,cb)=>{
  const res = createProxy(data)
  cb(res)
  return res
}
//使用案例
const obj = {
  d:'wei',
  a: {
    b: {
      c: {
        name: 'weiz'
      }
    }
  }
}
immerjs(obj,(data)=>{
  console.log(data.b===obj.b);//true
  data.b = {}
  console.log(data.b===obj.b);//false
})