javaScript实现多球运动

代码如下：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>多球运动</title>
    <style>
        *{margin:0;padding:0;}
        body{background-color: #90f;}
        .ball{position: absolute;left:0;top:0;width:100px;height:100px;background: #f0f;border-radius: 50%;}
    </style>
</head>
<body>
    <script>
        run(22)//封装
        //定义速度
        var speed;
        function run(num){
            //创建出num个div
            for(var i=0;i<num;i++){
                //[2,11) 随机速度
                speed = Math.floor(Math.random()*9+2);
                //创建生成节点
                var div = document.createElement("div");
                //添加类名
                div.className = 'ball'
                //自定义属性保存值
                div.speedX = Math.floor(Math.random()*9+2)
                div.speedY = Math.floor(Math.random()*9+2)
                //将div放置到body中
                document.body.appendChild(div)
            }
            //获取元素
            var box = document.getElementsByClassName( "ball" )
            //获取文档可视区域的宽高
            var maxX = document.documentElement.clientWidth - box[0].offsetWidth;
            var maxY = document.documentElement.clientHeight  - box[0].offsetHeight;
            //自适应窗口
            window.onresize = function(){
                maxX = document.documentElement.clientWidth - box[0].offsetWidth;
                maxY = document.documentElement.clientHeight  - box[0].offsetHeight;
            }
            play()
            function play(){
                for(var i=0;i<num;i++){
                    //获取
                    var ball = box[i];
                    var startTop = ball.offsetTop;
                    var startLift = ball.offsetLeft;
                    //startTop都为零；
                    var top = startTop + ball.speedY;
                    var left = startLift + ball.speedX;
                    //判断小球是否出左右边界
                    if(left <= 0 || left >= maxX){
                        //改变方向
                        ball.speedX = -ball.speedX;
                        ball.style.background=randomColor()
                        //判断
                        if(left <= 0){
                            left = 0;
                        }else if(left >= maxX){
                            left = maxX;
                        }
                    }
                    //判断小球是否出上下边界
                    if(top <= 0 || top >= maxY ){
                        // 改变方向；
                        ball.speedY = -ball.speedY;  
                        ball.style.background=randomColor()
                        //判断
                        if( top <= 0 ){
                            top = 0;
                        }else if( top >= maxY ){
                            top = maxY;
                        }
                    }
                    ball.style.top = top + "px";
                    ball.style.left = left + "px";                    
                }
                //执行动画帧
                requestAnimationFrame(play);
            }
            //颜色随机
            function randomColor() {
                var r = Math.floor(Math.random() * 256),
                    g = Math.floor(Math.random() * 256),
                    b = Math.floor(Math.random() * 256);
                    return "rgb(" + r + "," + g + "," + b + ")";
            }
        }
    </script>
</body>
</html>