1、在main.js同級建一個檔案directives.js

import Vue from 'vue';

// v-dialogDrag: 彈窗拖拽
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';

    // 獲取原有屬性 ie dom元素.currentStyle 火狐谷歌 window.getComputedStyle(dom元素, null);
    const sty = dragDom.currentStyle || window.getComputedStyle(dragDom, null);

    dialogHeaderEl.onmousedown = (e) => {
      // 滑鼠按下，計算當前元素距離可視區的距離
      const disX = e.clientX - dialogHeaderEl.offsetLeft;
      const disY = e.clientY - dialogHeaderEl.offsetTop;

      // 獲取到的值帶px 正則匹配替換
      let styL, styT;

      // 注意在ie中 第一次獲取到的值為元件自帶50% 移動之後賦值為px
      if (sty.left.includes('%')) {
        styL = +document.body.clientWidth * (+sty.left.replace(/\%/g, '') / 100);
        styT = +document.body.clientHeight * (+sty.top.replace(/\%/g, '') / 100);
      } else {
        styL = +sty.left.replace(/\px/g, '');
        styT = +sty.top.replace(/\px/g, '');
      };

      document.onmousemove = function (e) {
        // 通過事件委託，計算移動的距離
        const l = e.clientX - disX;
        const t = e.clientY - disY;

        // 移動當前元素
        dragDom.style.left = `${l + styL}px`;
        dragDom.style.top = `${t + styT}px`;

        //將此時的位置傳出去
        //binding.value({x:e.pageX,y:e.pageY})
      };

      document.onmouseup = function (e) {
        document.onmousemove = null;
        document.onmouseup = null;
      };
    }
  }
})

// v-dialogDragWidth: 彈窗寬度拖大 拖小
Vue.directive('dialogDragWidth', {
  bind(el, binding, vnode, oldVnode) {
    const dragDom = binding.value.$el.querySelector('.el-dialog');

    el.onmousedown = (e) => {

      // 滑鼠按下，計算當前元素距離可視區的距離
      const disX = e.clientX - el.offsetLeft;

      document.onmousemove = function (e) {
        e.preventDefault(); // 移動時禁用預設事件

        // 通過事件委託，計算移動的距離
        const l = e.clientX - disX;
        dragDom.style.width = `${l}px`;
      };

      document.onmouseup = function (e) {
        document.onmousemove = null;
        document.onmouseup = null;
      };
    }
  }
})
 

2、main.js新增引用

import './directives.js'

3、在需要用到拖拽功能的彈窗標籤上加 

v-dialogDrag

例如：

<el-dialog title="預覽" :visible.sync="viewDialogVisible"  v-dialogDrag>
</el-dialog>

即可