目录结构：

index.js:

import drag from './drag'

const install = function(Vue) {
  Vue.directive('el-drag-dialog', drag)
}

if (window.Vue) {
  window['el-drag-dialog'] = drag
  Vue.use(install); // eslint-disable-line
}

drag.install = install
export default drag

drag.js:

export default {
    bind(el, binding, vnode) {
      const dialogHeaderEl = el.querySelector('.el-dialog__header')
      const dragDom = el.querySelector('.el-dialog')
      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 getStyle = (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 dragDomWidth = dragDom.offsetWidth
        const dragDomHeight = dragDom.offsetHeight
  
        const screenWidth = document.body.clientWidth
        const screenHeight = document.body.clientHeight
  
        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 = getStyle(dragDom, 'left')
        let styT = getStyle(dragDom, 'top')
  
        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;`
  
          // emit onDrag event
          vnode.child.$emit('dragDialog')
        }
  
        document.onmouseup = function(e) {
          document.onmousemove = null
          document.onmouseup = null
        }
      }
    }
  }
  

调用：
import 引入
directives:注册
el-dialog :中 v-el-drag-dialog