sendMessage:function(){
            var _this = this;
            var userWords = document.createElement('li');
            var ulTag = document.querySelector('.list-box');

            userWords.innerHTML = "
"+ _this.userMessage +"
"
            userWords.setAttribute('class','talk users-words contact-box clearfix');
            ulTag.appendChild(userWords);
            ulTag.scrollTop = ulTag.scrollHeight; //此处不能赋值
            console.log(ulTag.scrollTop,ulTag.scrollHeight); 
        }
        
        
        我希望达到插入一个元素，内容区域自动滚动到底部