<template>
  <div id="app">
    <p ref="name">{{ name }}</p>
    <button @click="handleClick">修改name</button>
  </div>
</template>
<script>
  export default {
  name: 'App',
  data () {
    return {
      name: '井柏然'
    }
  },
  mounted() {
    console.log('mounted', this.$refs.name.innerText)
  },
  methods: {
    handleClick () {
      this.$nextTick(() => console.log('nextTick1', this.$refs.name.innerText))
      this.name = 'jngboran'
      console.log('sync log', this.$refs.name.innerText)
      this.$nextTick(() => console.log('nextTick2', this.$refs.name.innerText))
    }
  }
}
</script>

const callbacks = [] // 存放cb的隊(duì)列
let pending = false // 是否馬上遍歷隊(duì)列，執(zhí)行cb的標(biāo)志

function flushCallbacks () {
  pending = false // 注意這里，一旦執(zhí)行，pending馬上被重置為false
  const copies = callbacks.slice(0)
  callbacks.length = 0
  for (let i = 0; i < copies.length; i++) {
    copies[i]() // 執(zhí)行每個(gè)cb
  }
}

let timerFunc // nextTick異步實(shí)現(xiàn)fn
if (typeof Promise !== 'undefined' && isNative(Promise)) {
  // Promise方案
  const p = Promise.resolve()
  timerFunc = () => {
    p.then(flushCallbacks) // 將flushCallbacks包裝進(jìn)Promise.then中
  }
  isUsingMicroTask = true
} else if (!isIE && typeof MutationObserver !== 'undefined' && (
  isNative(MutationObserver) ||
  MutationObserver.toString() === '[object MutationObserverConstructor]'
)) {
  // MutationObserver方案
  let counter = 1
  const observer = new MutationObserver(flushCallbacks) // 將flushCallbacks作為觀測(cè)變化的cb
  const textNode = document.createTextNode(String(counter)) // 創(chuàng)建文本節(jié)點(diǎn)
  // 觀測(cè)文本節(jié)點(diǎn)變化
  observer.observe(textNode, {
    characterData: true
  })
  // timerFunc改變文本節(jié)點(diǎn)的data，以觸發(fā)觀測(cè)的回調(diào)flushCallbacks
  timerFunc = () => { 
    counter = (counter + 1) % 2
    textNode.data = String(counter)
  }
  isUsingMicroTask = true
} else if (typeof setImmediate !== 'undefined' && isNative(setImmediate)) {
  // setImmediate方案
  timerFunc = () => {
    setImmediate(flushCallbacks)
  }
} else {
  // 最終降級(jí)方案setTimeout
  timerFunc = () => {
    setTimeout(flushCallbacks, 0)
  }
}

const observer = new MutationObserver(() => console.log('觀測(cè)到文本節(jié)點(diǎn)變化'))
const textNode = document.createTextNode(String(1))
observer.observe(textNode, {
    characterData: true
})
console.log('script start')
setTimeout(() => console.log('timeout1'))
textNode.data = String(2) // 這里對(duì)文本節(jié)點(diǎn)進(jìn)行值的修改
console.log('script end')

export function nextTick (cb?: Function, ctx?: Object) {
  let _resolve
  // 往全局的callbacks隊(duì)列中添加cb
  callbacks.push(() => {
    if (cb) {
      try {
        cb.call(ctx)
      } catch (e) {
        handleError(e, ctx, 'nextTick')
      }
    } else if (_resolve) {
      // 這里是支持Promise的寫(xiě)法
      _resolve(ctx)
    }
  })
  if (!pending) {
    pending = true
    // 執(zhí)行timerFunc，在下一個(gè)Tick中執(zhí)行callbacks中的所有cb
    timerFunc()
  }
  // 對(duì)Promise的實(shí)現(xiàn)，這也是我們使用時(shí)可以寫(xiě)成nextTick.then的原因
  if (!cb && typeof Promise !== 'undefined') {
    return new Promise(resolve => {
      _resolve = resolve
    })
  }
}

this.$nextTick(() => console.log('nextTick1'))
this.$nextTick(() => console.log('nextTick2'))

// 用來(lái)存放Wathcer的隊(duì)列。注意，不要跟nextTick的callbacks搞混了，都是隊(duì)列，但用處不同～
const queue: Array<Watcher> = []
function queueWatcher (watcher: Watcher) {
  const id = watcher.id // 拿到Wathcer的id，這個(gè)id每個(gè)watcher都有且全局唯一
  if (has[id] == null) {
    // 避免添加重復(fù)wathcer，這也是異步渲染的優(yōu)化做法
    has[id] = true
    if (!flushing) {
      queue.push(watcher)
    }
    if (!waiting) {
      waiting = true
      // 這里把flushSchedulerQueue推進(jìn)nextTick的callbacks隊(duì)列中
      nextTick(flushSchedulerQueue)
    }
  }
}

function flushSchedulerQueue () {
  currentFlushTimestamp = getNow()
  flushing = true
  let watcher, id
  // 排序保證先父后子執(zhí)行更新，保證userWatcher在渲染W(wǎng)atcher前
  queue.sort((a, b) => a.id - b.id)
  // 遍歷所有的需要派發(fā)更新的Watcher執(zhí)行更新
  for (index = 0; index < queue.length; index++) {
    watcher = queue[index]
    id = watcher.id
    has[id] = null
    // 真正執(zhí)行派發(fā)更新，render -> update -> patch
    watcher.run()
  }
}

this.$nextTick(() => console.log('nextTick1', this.$refs.name.innerText))
this.name = 'jngboran'
console.log('sync log', this.$refs.name.innerText)
this.$nextTick(() => console.log('nextTick2', this.$refs.name.innerText))