关于vue.js:vue2611版本的nextTick

if (typeof Promise !== 'undefined' && isNative(Promise)) {const p = Promise.resolve()
  timerFunc = () => {p.then(flushCallbacks)
    // In problematic UIWebViews, Promise.then doesn't completely break, but
    // it can get stuck in a weird state where callbacks are pushed into the
    // microtask queue but the queue isn't being flushed, until the browser
    // needs to do some other work, e.g. handle a timer. Therefore we can
    // "force" the microtask queue to be flushed by adding an empty timer.
    if (isIOS) setTimeout(noop)
  }
  isUsingMicroTask = true
} else if (!isIE && typeof MutationObserver !== 'undefined' && (isNative(MutationObserver) ||
  // PhantomJS and iOS 7.x
  MutationObserver.toString() === '[object MutationObserverConstructor]'
)) {
  // Use MutationObserver where native Promise is not available,
  // e.g. PhantomJS, iOS7, Android 4.4
  // (#6466 MutationObserver is unreliable in IE11)
  let counter = 1
  const observer = new MutationObserver(flushCallbacks)
  const textNode = document.createTextNode(String(counter))
  observer.observe(textNode, {characterData: true})
  timerFunc = () => {counter = (counter + 1) % 2
    textNode.data = String(counter)
  }
  isUsingMicroTask = true
} else if (typeof setImmediate !== 'undefined' && isNative(setImmediate)) {
  // Fallback to setImmediate.
  // Technically it leverages the (macro) task queue,
  // but it is still a better choice than setTimeout.
  timerFunc = () => {setImmediate(flushCallbacks)
  }
} else {
  // Fallback to setTimeout.
  timerFunc = () => {setTimeout(flushCallbacks, 0)
  }
}

Promise > MutationObserver > setImmediate > setTimeout

MutationObserver 能监听一个 DOM 对象上产生的子节点删除、属性批改、文本内容批改等

let mo = new MutationObserver(callback);
let domTarget = 你想要监听的 dom 节点;
mo.observe(domTarget, {characterData: true // 阐明监听文本内容的批改。})

相熟工作执行机制就能理解