将注释的代码换上去不能正常运行，很难受
将timer定义在animate方法外面将所有的clearInterval(obj.timer)改成clearInterval(timer）
https://www.wenmi365.com/question/%E8%AF%B7%E6%95%99%E4%B8%80%E4%B8%AA%E9%97%AE%E9%A2%98%EF%BC%8C%E5%9C%A8%E5%86%99%E7%9B%92%E5%AD%90%E7%A7%BB%E5%8A%A8%E6%A1%88%E4%BE%8B%E7%9A%84%E6%97%B6%E5%80%99%EF%BC%8C%E4%B8%BA%E5%95%A5%E6%8D%A2/
