JS原生实现元素的拖拽

页面样式

<!DOCTYPE html>
<html>

<head lang="en">
  <meta charset="UTF-8">
  <title></title>
  <style>
    .login-header {
      width: 100%;
      text-align: center;
      height: 30px;
      font-size: 24px;
      line-height: 30px;
    }

    ul,
    li,
    ol,
    dl,
    dt,
    dd,
    div,
    p,
    span,
    h1,
    h2,
    h3,
    h4,
    h5,
    h6,
    a {
      padding: 0px;
      margin: 0px;
    }

    .login {
      width: 512px;
      position: absolute;
      border: #ebebeb solid 1px;
      height: 280px;
      left: 50%;
      right: 50%;
      background: #ffffff;
      box-shadow: 0px 0px 20px #ddd;
      z-index: 9999;
      margin-left: -250px;
      margin-top: 140px;
      display: none;
    }

    .login-title {
      width: 100%;
      margin: 10px 0px 0px 0px;
      text-align: center;
      line-height: 40px;
      height: 40px;
      font-size: 18px;
      position: relative;
      cursor: move;
      -moz-user-select: none;
      /*火狐*/
      -webkit-user-select: none;
      /*webkit浏览器*/
      -ms-user-select: none;
      /*IE10*/
      -khtml-user-select: none;
      /*早期浏览器*/
      user-select: none;
    }

    .login-input-content {
      margin-top: 20px;
    }

    .login-button {
      width: 50%;
      margin: 30px auto 0px auto;
      line-height: 40px;
      font-size: 14px;
      border: #ebebeb 1px solid;
      text-align: center;
    }

    .login-bg {
      width: 100%;
      height: 100%;
      position: fixed;
      top: 0px;
      left: 0px;
      background: #000000;
      filter: alpha(opacity=30);
      -moz-opacity: 0.3;
      -khtml-opacity: 0.3;
      opacity: 0.3;
      display: none;
    }

    a {
      text-decoration: none;
      color: #000000;
    }

    .login-button a {
      display: block;
    }

    .login-input input.list-input {
      float: left;
      line-height: 35px;
      height: 35px;
      width: 350px;
      border: #ebebeb 1px solid;
      text-indent: 5px;
    }

    .login-input {
      overflow: hidden;
      margin: 0px 0px 20px 0px;
    }

    .login-input label {
      float: left;
      width: 90px;
      padding-right: 10px;
      text-align: right;
      line-height: 35px;
      height: 35px;
      font-size: 14px;
    }

    .login-title span {
      position: absolute;
      font-size: 12px;
      right: -20px;
      top: -30px;
      background: #ffffff;
      border: #ebebeb solid 1px;
      width: 40px;
      height: 40px;
      border-radius: 20px;
    }
  </style>
</head>

<body>
  <div class="login-header"><a id="link" href="javascript:void(0);">点击，弹出登录框</a></div>
  <div id="login" class="login">
    <div id="title" class="login-title">登录会员
      <span><a id="closeBtn" href="javascript:void(0);" class="close-login">关闭</a></span></div>
    <div class="login-input-content">
      <div class="login-input">
        <label>用户名：</label>
        <input type="text" placeholder="请输入用户名" name="info[username]" id="username" class="list-input">
      </div>
      <div class="login-input">
        <label>登录密码：</label>
        <input type="password" placeholder="请输入登录密码" name="info[password]" id="password" class="list-input">
      </div>
    </div>
    <div id="loginBtn" class="login-button"><a href="javascript:void(0);" id="login-button-submit">登录会员</a></div>
  </div>
  <!--登录框-->
  <div id="bg" class="login-bg"></div>
  <!--遮挡层-->

</body>

</html>

脚本文件

/**
 * 获取指定标签对象
 * @param id 标签的id属性值
 * @returns {Element}根据id属性值返回指定标签对象
 */
function my$(id) {
    return document.getElementById(id);
}
//点击超链接弹出登录框,点击页面的任何位置都可以关闭登录框
my$("link").onclick = function (e) {
  my$("login").style.display = "block";
  my$("bg").style.display = "block";
  e.stopPropagation();
  console.log('出现');

};
//获取关闭,注册点击事件,隐藏登录框和遮挡层
my$("closeBtn").onclick = function () {
  my$("login").style.display = "none";
  my$("bg").style.display = "none";
};

//按下鼠标,移动鼠标,移动登录框
my$("title").onmousedown = function (e) {
  //获取此时的可视区域的横坐标-此时登录框距离左侧页面的横坐标
  var spaceX = e.clientX - my$("login").offsetLeft;
  var spaceY = e.clientY - my$("login").offsetTop;
  // 移动事件
  document.onmousemove = function (e) {
    // 获取页面宽高
    var bodyW = document.documentElement.clientWidth
    var bodyH = document.documentElement.clientHeight
    // 获取盒子宽高
    var loginH = my$('login').offsetHeight
    var loginW = my$('login').offsetWidth
    // 获取关闭按钮多出来的宽高,只要一半就行
    var btnH = my$('closeBtn').parentNode.offsetHeight / 2
    var btnW = my$('closeBtn').parentNode.offsetWidth / 2


    // 新的可视区域的横坐标-spaceX====>新的值--->登录框的left属性
    // 同时对可移动范围进行限制
    var loginX, loginY
    // 限制横向区域移动范围
    if (e.clientX - spaceX <= 0) {
      loginX = 0
    } else if (e.clientX - spaceX > 0 && e.clientX - spaceX <= bodyW - loginW - btnW) {
      loginX = e.clientX - spaceX
    } else {
      loginX = bodyW - loginW - btnW
    }

    // 限制纵向区域移动范围
    if (e.clientY - spaceY <= btnH) {
      loginY = btnH
    } else if (e.clientY - spaceY > 0 && e.clientY - spaceY <= bodyH - loginH) {
      loginY = e.clientY - spaceY
    } else {
      loginY = bodyH - loginH
    }
    // 加上外边距就实现点哪儿是哪儿了
    var x = loginX + 250
    var y = loginY - 140

    my$('login').style.left = x + 'px'
    my$('login').style.top = y + 'px'
  }
}

document.onmouseup = function () {
  document.onmousemove = null; //当鼠标抬起的时候,把鼠标移动事件干掉
};

示例演示