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;
            };
         return false
        }  
    }
})

main.js:

1. // 引入自定义指令

2. import './directives.js';

用法

<template>
    <el-dialog
        v-dialogDrag
        ref="dialog__wrapper">
        <div class="dialog-body">
            
            <div 
                class="line"
                v-dialogDragWidth="$refs.dialog__wrapper"></div>
        </div>
    </el-dialog>
</template>