尽管是 hack，但此简单功能会持续侦听目录。 （通过setTimeout）更改元素的高度并在检测到更改时触发回调。

Although a "hack", this simple function continuously "listens" (through setTimeout) to changes in an element's height and fire a callback when a change was detected.

重要的是要考虑元素的 height 可能会变化用户执行的任何操作（调整大小，点击等），因此，由于无法知道是什么会引起高度变化，因此可以完成所有操作绝对保证100％的检测是放置一个间隔高度检查器：

It's important to take into account an element's height might change regardless of any action taken by a user (resize, click, etc.) and so, since it is impossible to know what can cause a height change, all that can be done to absolutely guarantee 100% detection is to place an interval height checker :

function onElementHeightChange(elm, callback) {
  var lastHeight = elm.clientHeight, newHeight;

  (function run() {
    newHeight = elm.clientHeight;
    if (lastHeight != newHeight)
      callback(newHeight)
    lastHeight = newHeight

    if (elm.onElementHeightChangeTimer)
      clearTimeout(elm.onElementHeightChangeTimer)

    elm.onElementHeightChangeTimer = setTimeout(run, 200)
  })()
}

// to clear the timer use:
// clearTimeout(document.body.onElementHeightChangeTimer);

// DEMO:
document.write("click anywhere to change the height")

onElementHeightChange(document.body, function(h) {
  console.log('Body height changed:', h)
})

window.addEventListener('click', function() {
  document.body.style.height = Math.floor((Math.random() * 5000) + 1) + 'px'
})