原生JavaScript实现小球弹性碰撞动画

<style> //style样式
        * {
            margin: 0;
            padding: 0;
        }

        #box {
            width: 500px;
            height: 600px;
            background-color: #eee;
            box-shadow: 0 0 10px 0 #000;
            margin: auto;
            overflow: hidden;
            position: relative;
            margin-top: 50px;
        }

        #box div {
            width: 50px;
            height: 50px;
            border-radius: 50%;
            background-color: #fff;
            position: absolute;
        }
    </style>
    <body>
    <div id="box">
        <div id="cir"></div>
        <div></div>
        <div></div>
        <div></div>
        <div></div>
        <div></div>
        <div></div>
    </div>
</body>
<script>
var box = document.getElementById("box");
var cir = document.getElementById("cir")
var cirs = box.querySelectorAll("div");
collMove(box, cir, 6);
collMove(box, cirs[1], 7);
collMove(box, cirs[2], 8);
collMove(box, cirs[3], 9);
collMove(box, cirs[4], 10);
collMove(box, cirs[5], 10);
collMove(box, cirs[6], 11);
/**
 * 元素遇边界弹开
 * 弹开的同时改变元素颜色
 * @param {容器获取} box 
 * @param {容器内弹跳元素获取} cir 
 * @param {弹跳速度} speed 
 */
function collMove(box, cir, speed) {//方法封装
    var oDiv = box; //获取容器
    var oCir = cir; //获取容器内元素
    var xMax = oDiv.offsetWidth - oCir.offsetWidth; //容器最大X轴边界
    var yMax = oDiv.offsetHeight - oCir.offsetHeight; //容器最大Y轴边界
    var motionX = 0; //元素X轴坐标初始化
    var motionY = 0; //元素y轴坐标初始化
    (() => {
        var speedX = speed; //x轴偏移量
        var speedY = speed; //y轴偏移量
        setInterval(() => {
            motionX += speedX; //进行X轴偏移
            motionY += speedY; //进行y轴偏移
            if (motionX >= xMax) { //检测是否碰到X轴右边界
                motionX = xMax; //碰到边界将X轴坐标设为x轴最大右边界
                speedX = -speedX; //x轴偏移量反转
                randColor(oCir); //改变颜色
            } else if (motionX <= 0) { //检测是否碰到X左边界
                motionX = 0; //碰到边界将X轴坐标设为 0 即左边界初始位置
                speedX = -speedX; //再次反转X轴偏移量
                randColor(oCir); //下方上下边界检测同理
            }
            if (motionY >= yMax) {
                motionY = yMax;
                speedY = -speedY
                randColor(oCir);
            } else if (motionY <= 0) {
                motionY = 0;
                speedY = -speedY;
                randColor(oCir);
            }
            oCir.style.marginLeft = motionX + "px"; //设置元素X轴坐标
            oCir.style.marginTop = motionY + "px"; //设置元素Y轴坐标
        }, 10);
    })();

    function randColor(obj) { //封装一个随机色彩，改变颜色直接调用
        var op = Math.random() * 7 + 3;

        function color() {
            return Math.floor(Math.random() * 256);
        }
        return obj.style.backgroundColor = `rgba(${color()},${color()},${color()},${op})`;
    }
}
</script>

for(var i = 1 ; i<=10;i++){
 collMove(box,cirs[i],i);
}