[ 记录 ] 观察者Dom的变化

```js
 // Firefox和Chrome早期版本中带有前缀
    var MutationObserver = window.MutationObserver || window.WebKitMutationObserver || window.MozMutationObserver
    // 选择目标节点
    var target = formDoms[4].dom// document.querySelector('#some-id'); 
    // 创建观察者对象
    var observer = new MutationObserver(function (mutations) {
  mutations.forEach(function (mutation) {
      console.log(mutation);
  });
    });
    // 配置观察选项:
    var config = { attributes: true, childList: true, characterData: true, subtree: true }
    // 传入目标节点和观察选项
    observer.observe(target, config);
```