element-ui对话框可拖拽的功能如何实现？

import Vue from 'vue'; // v-dialogDrag: 弹窗拖拽属性Vue.directive('dialogDrag', {    bind(el, binding, vnode, oldVnode) {        const dialogHeaderEl = el.querySelector('.el-dialog__header');        const dragDom = el.querySelector('.el-dialog');        //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;                                const minDragDomTop = dragDom.offsetTop;                const maxDragDomTop = screenHeight - dragDom.offsetTop - dragDomheight;                         // 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('%')) {                styL = +document.body.clientWidth * (+styL.replace(/\%/g, '') / 100);                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;            };        }      }})

document.body.clientWidth  //BODY对象宽度document.body.clientHeight //BODY对象高度document.documentElement.clientWidth  //可见区域宽度document.documentElement.clientHeight //可见区域高度

// 引入Dialog可拖拽，注意文件所在目录。目前尚未发现引入的先后关系，若有再补充import './directives.js';

<el-dialog></el-dialog>