a-modal 弹窗可拖拽，解决网上已知的坑

1.弹窗可拖拽，网上代码几乎一致，但都存在同一个问题，那就是拖动完成后，如果选中了文字，（像是下面这种情况，图1），然后再次拖动，松开鼠标左键后，鼠标不点击的情况下移动弹窗就会自动跟随着。

对于一些开发者来说这可能不算问题，但是总觉得挺别扭，于是参考element Plus，发现新增了可拖动弹窗，F12查看html结构发现一个重要的css样式，user-select(图2所示)

图1

图2

附源代码：

import Vue from 'vue'
 
// 弹窗拖拽属性
/**
 * @directive 自定义属性
 * @todo 弹窗拖拽属性
 * @desc 使用在弹窗内部任意加载的html添加v-drag
 * @param .ant-modal-header 弹窗头部用来拖动的属性
 * @param .ant-modal 拖动的属性
*/
Vue.directive('drag-modal', (el, binding, vnode, oldVnode) => {
     
    // inserted (el, binding, vnode, oldVnode) {
    Vue.nextTick(() => {
        const isThemeModal = el.classList.contains('grid-theme')
        console.log(isThemeModal);
        const dialogHeaderEl = isThemeModal ? el.querySelector('.ant-tabs-bar') : document.querySelector('.ant-modal-header')
        dialogHeaderEl.style.userSelect='none' //
        const dragDom = isThemeModal ? el.querySelector('.ant-modal') : document.querySelector('.ant-modal')
        // dialogHeaderEl.style.cursor = 'move';
        dialogHeaderEl.style.cssText += ';cursor:move;'
        // dragDom.style.cssText += ';top:0px;'
 
        // 获取原有属性 ie dom元素.currentStyle 火狐谷歌 window.getComputedStyle(dom元素, null);
        const sty = (function () {
            if (window.document.currentStyle) {
                return (dom, attr) => dom.currentStyle[attr]
            } else {
                return (dom, attr) => getComputedStyle(dom, false)[attr]
            }
        })()
 
        dialogHeaderEl.onmousedown = (e) => {
             
            // 鼠标按下，计算当前元素距离可视区的距离
            const disX = e.clientX - dialogHeaderEl.offsetLeft
            const disY = e.clientY - dialogHeaderEl.offsetTop
 
            const screenWidth = document.body.clientWidth // body当前宽度
            const screenHeight = document.documentElement.clientHeight // 可见区域高度(应为body高度，可某些环境下无法获取)
 
            const dragDomWidth = dragDom.offsetWidth // 对话框宽度
            const dragDomheight = dragDom.offsetHeight // 对话框高度
 
            const minDragDomLeft = dragDom.offsetLeft
            const maxDragDomLeft = screenWidth - dragDom.offsetLeft - dragDomWidth - (isThemeModal ? 10 : 0)
 
            const minDragDomTop = dragDom.offsetTop
            const maxDragDomTop = screenHeight - dragDom.offsetTop - dragDomheight - (isThemeModal ? 10 : 0)
 
            // 获取到的值带px 正则匹配替换
            let styL = sty(dragDom, 'left')
            let styT = sty(dragDom, 'top')
 
            // 注意在ie中 第一次获取到的值为组件自带50% 移动之后赋值为px
            if (styL.includes('%')) {
                // eslint-disable-next-line no-useless-escape
                styL = +document.body.clientWidth * (+styL.replace(/\%/g, '') / 100)
                // eslint-disable-next-line no-useless-escape
                styT = +document.body.clientHeight * (+styT.replace(/\%/g, '') / 100)
            } else {
                styL = +styL.replace(/\px/g, '')
                styT = +styT.replace(/\px/g, '')
            };
 
            document.onmousemove = function (e) {
                // 通过事件委托，计算移动的距离
                let left = e.clientX - disX
                let top = e.clientY - disY
 
                // 边界处理
                if (-(left) > minDragDomLeft) {
                    left = -(minDragDomLeft)
                } else if (left > maxDragDomLeft) {
                    left = maxDragDomLeft
                }
 
                if (-(top) > minDragDomTop) {
                    top = -(minDragDomTop)
                } else if (top > maxDragDomTop) {
                    top = maxDragDomTop
                }
                // 移动当前元素
                dragDom.style.cssText += `;left:${left + styL}px;top:${top + styT}px;`
            }
 
            document.onmouseup = function (e) {
                document.onmousemove = null
                document.onmouseup = null
 
            }
 
        }
 
    })
})