网页包括一个按钮；

　　点击按钮，向页面中添加一条小鱼（用图片实现）；

　　小鱼在屏幕内随机方向移动，碰壁后转换方向继续移动；

　　当再次点击按钮，转步骤2，此时屏幕上多出一个小鱼；

　　-Web page includes a button

Click the button to add a fish to the page (with pictures to achieve)

Fish move randomly around the screen, change the direction to continue moving after hitting the wall

When click the button again and go to step 2, this time more than a small fish on the screen