dom元素改变监听

 function domChange(domId, callback) {
            // select the target node
            var target = document.getElementById(domId);
            // create an observer instance
            var observer = new MutationObserver(function (mutations) {
                mutations.forEach(function (mutation) {
                    callback();
                });
            });
            // configuration of the observer:
            var config = { attributes: true, childList: true, characterData: true };
            // pass in the target node, as well as the observer options
            observer.observe(target, config);
            // later, you can stop observing
            //observer.disconnect();
        }