JavaScript实现简单的拖拽效果

* {            margin: 0;            padding: 0;        }                p {            background: skyblue;            text-align: center;        }                html,        body {            width: 100%;            height: 100%;        }                .mask {            width: 100%;            height: 100%;            position: fixed;            left: 0;            top: 0;            background: rgba(0, 0, 0, .5);            display: none;        }                .login {            width: 400px;            height: 300px;            background: purple;            position: absolute;            left: 50%;            top: 50%;            transform: translate(-50%, -50%);            display: none;            cursor: move;        }                .login>span {            display: inline-block;            width: 50px;            height: 50px;            background: red;            position: absolute;            top: 0;            right: 0;        }

<p>我是p标签</p>    <a href="http://www.baidu.com" >官网</a>    <div class="mask"></div>    <div class="login">        <span></span></div>

//1.拿到需要操作的元素const oP = document.querySelector("p");const oMask = document.querySelector(".mask");const oLogin = document.querySelector(".login");const oClose = oLogin.querySelector(".login>span");// console.log(oClose); //2.监听点击事件oP.onclick = function() {    oMask.style.display = "block";    oLogin.style.display = "block";        };        oClose.onclick = function() {            oMask.style.display = "none";            oLogin.style.display = "none";        }; //3.监听登录框的按下和移动事件oLogin.onmousedown = function(e) {            e = e || e.window;             //1.计算固定不变的距离            const x = e.pageX - oLogin.offsetLeft;            const y = e.pageY - oLogin.offsetTop;            // console.log(x);             //2.监听移动事件            oLogin.onmousemove = function(e) {                e = e || e.window;                 //3.计算移动之后的偏移位                let offsetX = e.pageX - x;                let offsetY = e.pageY - y;                 //4.重新设置登录框的位置                oLogin.style.left = offsetX + 'px';                oLogin.style.top = offsetY + 'px';            };        };         oLogin.onmouseup = function() {            oLogin.onmousemove = null;        };