詳解Vue3的響應式原理解析

// 1.對象響應化：遍歷每個key，定義getter、setter
// 2.數組響應化：覆蓋數組原型方法，額外增加通知邏輯
const originalProto = Array.prototype
const arrayProto = Object.create(originalProto)
  ;['push', 'pop', 'shift', 'unshift', 'splice', 'reverse', 'sort'].forEach(
    method => {
      arrayProto[method] = function () {
        originalProto[method].apply(this, arguments)
        notifyUpdate()
      }
    }
  )
function observe (obj) {
  if (typeof obj !== 'object' || obj == null) {
    return
  }
  // 增加數組類型判斷，若是數組則覆蓋其原型
  if (Array.isArray(obj)) {
    Object.setPrototypeOf(obj, arrayProto)
  } else {
    const keys = Object.keys(obj)
    for (let i = 0; i < keys.length; i++) {
      const key = keys[i]
      defineReactive(obj, key, obj[key])
    }
  }
}
function defineReactive (obj, key, val) {
  observe(val) // 解決嵌套對象問題
  Object.defineProperty(obj, key, {
    get () {
      return val
    },
    set (newVal) {
      if (newVal !== val) {
        observe(newVal) // 新值是對象的情況
        val = newVal
        notifyUpdate()
      }
    }
  })
}
function notifyUpdate () {
  console.log('頁面更新!')
}

function reactive (obj) {
  if (typeof obj !== 'object' && obj != null) {
    return obj
  }
  // Proxy相當於在對象外層加攔截
  // http://es6.ruanyifeng.com/#docs/proxy
  const observed = new Proxy(obj, {
    get (target, key, receiver) {
      // Reflect用於執行對象默認操作，更規范、更友好
      // Proxy和Object的方法Reflect都有對應
      // http://es6.ruanyifeng.com/#docs/reflect
      const res = Reflect.get(target, key, receiver)
      console.log(`獲取${key}:${res}`)
      return res
    },
    set (target, key, value, receiver) {
      const res = Reflect.set(target, key, value, receiver)
      console.log(`設置${key}:${value}`)
      return res
    },
    deleteProperty (target, key) {
      const res = Reflect.deleteProperty(target, key)
      console.log(`刪除${key}:${res}`)
      return res
    }
  })
  return observed
}
//代碼測試
const state = reactive({
  foo: 'foo',
  bar: { a: 1 }
})
// 1.獲取
state.foo // ok
// 2.設置已存在屬性
state.foo = 'fooooooo' // ok
// 3.設置不存在屬性
state.dong = 'dong' // ok
// 4.刪除屬性
delete state.dong // ok

// 設置嵌套對象屬性
react.bar.a = 10 // no ok

      // 提取幫助方法
      const isObject = val => val !== null && typeof val === 'object'
      function reactive (obj) {
        //判斷是否對象
        if (!isObject(obj)) {
          return obj
        }
        const observed = new Proxy(obj, {
          get (target, key, receiver) {
            // ...
            // 如果是對象需要遞歸
            return isObject(res) ? reactive(res) : res
          },
          //...
        }

const toProxy = new WeakMap() // 形如obj:observed
      const toRaw = new WeakMap() // 形如observed:obj
      function reactive (obj) {
        //...
        // 查找緩存，避免重復代理
        if (toProxy.has(obj)) {
          return toProxy.get(obj)
        }
        if (toRaw.has(obj)) {
          return obj
        }
        const observed = new Proxy(...)
        // 緩存代理結果
        toProxy.set(obj, observed)
        toRaw.set(observed, obj)
        return observed
      }
      // 測試效果
      console.log(reactive(data) === state)
      console.log(reactive(state) === state)