可拖动弹窗，原生js实现code

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<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>可拖动弹窗</title>
    <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap@3.3.7/dist/css/bootstrap.min.css">
    <style>
        body {background: #f5f5f5; font-size: 14px; color: #333; }
        .dialog_btn_wrap {padding: 100px; text-align: center; }
        #mask {position: fixed; width: 100%; height: 100%; top: 0; left: 0; z-index: 1; background: rgba(0,0,0,.4); display: none;
            -moz-user-select: none; -webkit-user-select: none;}
        #dialog {position: absolute; width: 250px; height: 200px; top: 0; left: 0; border-radius: 10px; z-index: 2; background: #fff; display: none;
            -moz-user-select: none; -webkit-user-select: none;}
        .dialog_head {text-align: center; line-height: 50px; background-color: #ddd; cursor: move; }
        .dialog-body {height: 100px; }
        .dialog-foot {height: 50px; text-align: center; line-height: 50px; background-color: #ddd; }
    </style>
</head>
<body>

<div class="dialog_btn_wrap">
    <a class="btn btn-lg btn-primary" id="dialog_btn">弹窗</a>
</div>

<!--蒙层-->
<div id="mask"></div>

<!--弹窗-->
<div id="dialog">
    <div class="dialog_head" id="move_part">可拖拽区域</div>
    <div class="dialog-body"></div>
    <div class="dialog-foot">
        <a class="btn btn-default" id="dialog_close">关闭</a>
    </div>
</div>

<script>
    //g()函数用于获取dom对象
    function g(id) {
        return document.getElementById(id);
    }

    //点击弹出弹窗
    g('dialog_btn').onclick = function () {
        g('mask').style.display = 'block';
        g('dialog').style.display = 'block';
        autoCenter(g('dialog'));
    }

    //点击关闭弹窗
    g('dialog_close').onclick = function () {
        g('mask').style.display = 'none';
        g('dialog').style.display = 'none';
    }
    
    //弹窗自动居中
    function autoCenter(el) {
        //获取窗口宽高
        var windowW = document.documentElement.clientWidth;
        var windowH = document.documentElement.clientHeight;

        //获取弹窗宽高
        var elW = el.offsetWidth;
        var elH = el.offsetHeight;

        el.style.left = (windowW-elW)/2 + 'px';
        el.style.top = (windowH-elH)/2 + 'px';
    }

    //禁止选中弹窗内容
    //document.attachEvent IE浏览器监听事件，拖拽时禁止选中，firefox、chrome通过css -moz-user-select: none; -webkit-user-select: none;设置
    if(document.attachEvent) {
        g('dialog').attachEvent('onselectstart', function () {
            return false;
        })
    }

    //改变窗口大小，弹窗自动居中
    window.onresize = function () {
        autoCenter(g('dialog'));
    }

    //拖拽实现原理
    //1.鼠标点击时，设置弹窗可拖动，记录鼠标初试位置
    //2.鼠标拖动时，根据鼠标新位置更新弹窗位置
    //3.鼠标离开时，设置弹窗不可拖动
    //4.限制弹窗拖拽范围

    var mx = 0; //鼠标x,y轴坐标(相对于left top)
    var my = 0;

    var dx = 0; //弹窗x,y轴坐标
    var dy = 0;

    var isDraging = false; // 弹窗不可拖动

    //鼠标点击
    g('move_part').addEventListener('mousedown', function (e) {
        var e = e || window.event; //兼容写法，window.event为IE浏览器独有对象
        mx = e.pageX; //点击时鼠标X坐标
        my = e.pageY; //点击时鼠标Y坐标
        dx = g('dialog').offsetLeft; //弹窗距页面左侧距离
        dy = g('dialog').offsetTop; //弹窗距页面顶部距离
        isDraging = true; //标记弹窗可拖动
    })

    //鼠标拖动
    //当鼠标在当前对象上移动时就产生了onmousemove事件
    document.onmousemove = function (e) {
        var e = e || window.event;
        var x = e.pageX; //移动时鼠标X坐标
        var y = e.pageY; //移动时鼠标X坐标
        if(isDraging) {
            var moveX = x - mx + dx; //位移值+弹窗left值=移动后弹窗left值
            var moveY = y - my + dy; //移动后弹窗top值

            //限制弹窗拖拽范围
            //页面宽高
            var pageW = document.documentElement.clientWidth;
            var pageH = document.documentElement.clientHeight;
            //弹窗宽高
            var dialogW = g('dialog').offsetWidth;
            var dialogH = g('dialog').offsetHeight;
            var maxX = pageW - dialogW; //x轴可拖动最大值
            var maxY = pageH - dialogH; //x轴可拖动最大值
            //Math.min()  Math.max()妙用
            moveX = Math.min(Math.max(0, moveX), maxX); //设定left范围, 0-maxX
            moveY = Math.min(Math.max(0, moveY), maxY); //设定top范围, 0-maxY
            //重新设置弹窗位置
            g('dialog').style.left = moveX + 'px';
            g('dialog').style.top = moveY + 'px';
        }
    }

    //鼠标离开
    g('move_part').addEventListener('mouseup', function () {
        isDraging = false;
    })

</script>
</body>
</html>
可拖动弹窗，原生js实现code

echeverra

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