JS案例：小球拖动，记录轨迹，并原路返回<meta name="viewport" content="width=dev

附上代码：

<!DOCTYPE html>
<html lang="en">

    <head>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <meta http-equiv="X-UA-Compatible" content="ie=edge">
        <title>Document</title>
        <style>
            .box {
                width: 100px;
                height: 100px;
                position: absolute;
                background: lightcoral;
                border-radius: 50%;
            }
        </style>
    </head>
    <body>
        <script>
            var arrX = [];//新建数组，记录小球的x轴路径
            var arrY = [];//新建数组，记录小球的y轴路径
            var i = 0;//小球移动时数组的第i项存进数组
            var stop;//小球的运动
            function Ball() {}//新建小球类
            Ball.prototype = {
                ball:null,//新建小球
                createBall: function () {//创建小球，添加到body中
                    this.ball = document.createElement("div");
                    document.body.appendChild(this.ball);
                    this.ball.className = "box";
                    this.ball.self = this;//引入小球的属性self指向Ball对象（this）
                    this.ball.addEventListener("mousedown", this.mouseHandler);//添加点击事件
                    return this.ball;
                },
                mouseHandler: function (e) {
                    if (e.type === "mousedown") {//当鼠标点击时添加移动事件给document，添加鼠标松开事件给小球，并且使用回调，每次执行一个函数，对e.type进行判断
                        this.addEventListener("mouseup", this.self.mouseHandler);
                        document.ball = this;//引入对象ball给document
                        document.boxObj = {//给document添加对象属性鼠标相对小球位置
                            x: e.offsetX,
                            y: e.offsetY
                        };
                        document.addEventListener("mousemove", this.self.mouseHandler);
                    } else if (e.type === "mousemove") {//鼠标移动时让小球位置等于鼠标在当前窗口的位置减去鼠标相对小球位置
                        this.ball.style.left = e.x - this.boxObj.x + "px";
                        this.ball.style.top = e.y - this.boxObj.y + "px";
                        arrX.push(this.ball.style.left);//小球每次移动将位置存入数组中
                        arrY.push(this.ball.style.top);
                    } else if (e.type === "mouseup") {//当鼠标松开时，解除监听事件并且执行自动返回函数
                        this.removeEventListener("mouseHandler", this.self.mouseHandler);
                        document.removeEventListener("mousemove", this.self.mouseHandler);
                        document.self = this;
                        i = arrX.length;
                        stop = setInterval(this.self.autoMove, 16);
                    }
                },
                autoMove: function () {//返回函数，当小球运动到初始状态时，取消Interval函数
                    document.self.style.left = arrX[i];
                    document.self.style.top = arrY[i];
                    if (i <= 0) {
                        arrX.length = 0;
                        arrY.length = 0;
                        clearInterval(stop);
                        return;
                    }
                    i--;
                }
            };
            //实例化小球，并且执行小球方法
            var ball = new Ball();
            ball.createBall();
        </script>
    </body>

</html>