需求：vue项目 element 的 dialog 弹出窗口加上 最大化 还原 和自定义拖拽、拉伸弹窗

原理是 利用vue 的自定义指令功能 自定义一个指令；

export default {
  bind(el, binding, vnode, oldVnode) {
    let resizeEvent = new CustomEvent('drag-resize',{detail:'尺寸变化',bubbles:false});
    //初始化不最大化
    el.fullscreen = false;
    //弹框可拉伸最小宽高
    let minWidth = 400;
    let minHeight = 300;
    //当前宽高
    let nowWidth = minWidth;
    let nowHight = minHeight;
    //当前顶部高度
    let nowMarginTop = 0;
    //获取弹框头部（这部分可双击全屏）
    const dialogHeaderEl = el.querySelector('.el-dialog__header');
    let hasSetBodyHight = false;
    //弹窗
    const dragDom = el.querySelector('.el-dialog');
    dragDom.className += ' el-drag-dialog';
    //清除选择头部文字效果
    dialogHeaderEl.onselectstart = new Function("return false");
    //头部加上可拖动cursor
    dialogHeaderEl.style.cursor = 'move';

    // 获取原有属性 ie dom元素.currentStyle 火狐谷歌 window.getComputedStyle(dom元素, null);
    const sty = dragDom.currentStyle || window.getComputedStyle(dragDom, null);

    //头部插入最大化最小化元素
    let maxMin = document.createElement("button");
    maxMin.className += ' el-dialog__headerbtn el-dialog__minmax';
    maxMin.style.right = '40px';
    maxMin.style.color = '#909399';
    maxMin.title = el.fullscreen ? '还原' : '最大化';
    maxMin.innerHTML = '<i class=' + (el.fullscreen ? '"el-icon-crop"' : '"el-icon-full-screen"') + ' onMouseOver="this.style.color=\'#409EFF\'" onMouseOut="this.style.color=\'inherit\'"></i>';
    dialogHeaderEl.insertBefore(maxMin, dialogHeaderEl.childNodes[1]);
    let moveDown = (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;

      // 获取到的值带px 正则匹配替换
      let styL, styT;

      // 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 (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) {
        // 通过事件委托，计算移动的距离
        const l = e.clientX - disX;
        const t = e.clientY - disY;

        // 移动当前元素
        dragDom.style.left = `${l + styL}px`;
        dragDom.style.top = `${t + styT}px`;

        //将此时的位置传出去
        //binding.value({x:e.pageX,y:e.pageY})
      };

      document.onmouseup = function (e) {
        document.onmousemove = null;
        document.onmouseup = null;
      };
    }
    dialogHeaderEl.onmousedown = moveDown;
    let bodyHeight = 'auto';

    function setMaxMin() {
      if (el.fullscreen) {
        let i = maxMin.querySelector('.el-icon-crop');
        i.classList.remove('el-icon-crop');
        i.classList.add('el-icon-full-screen');
        maxMin.innerHTML = '<i class="el-icon-full-screen"></i>';
        maxMin.title = '最大化';
        dragDom.style.height = "auto";
        dragDom.style.width = nowWidth + 'px';
        dragDom.style.marginTop = nowMarginTop;
        el.fullscreen = false;
        dialogHeaderEl.style.cursor = 'move';
        dialogHeaderEl.onmousedown = moveDown;
        dragDom.querySelector('.el-dialog__body').style.height = bodyHeight;
        hasSetBodyHight = false;
      } else {
        let i = maxMin.querySelector('.el-icon-full-screen');
        i.classList.remove('el-icon-full-screen');
        i.classList.add('el-icon-crop');
        maxMin.title = '还原';
        bodyHeight = dragDom.querySelector('.el-dialog__body').offsetHeight + 'px';
        nowHight = dragDom.clientHeight;
        nowWidth = dragDom.clientWidth;
        nowMarginTop = dragDom.style.marginTop;
        dragDom.style.left = 0;
        dragDom.style.top = 0;
        dragDom.style.height = "100VH";
        dragDom.style.width = "100VW";
        dragDom.style.marginTop = 0;
        el.fullscreen = true;
        dialogHeaderEl.style.cursor = 'initial';
        dialogHeaderEl.onmousedown = null;
        if (!hasSetBodyHight) {
          let footerHeight = dragDom.querySelector('.el-dialog__footer') && dragDom.querySelector('.el-dialog__footer').offsetHeight;
          dragDom.querySelector('.el-dialog__body').style.height = 'calc(100% - ' + (dialogHeaderEl.offsetHeight + footerHeight) + 'px)';
          hasSetBodyHight = true;
        }
      }
      el.dispatchEvent(resizeEvent);
    }

    //点击放大缩小效果
    maxMin.onclick = setMaxMin;
    //双击头部效果
    dialogHeaderEl.ondblclick = setMaxMin;
    //拉伸
    let resizeEl = document.createElement("div");
    dragDom.appendChild(resizeEl);
    //在弹窗右下角加上一个10-10px的控制块
    resizeEl.style.cursor = 'se-resize';
    resizeEl.style.position = 'absolute';
    resizeEl.style.height = '10px';
    resizeEl.style.width = '10px';
    resizeEl.style.right = '0px';
    resizeEl.style.bottom = '0px';
    //鼠标拉伸弹窗
    resizeEl.onmousedown = (e) => {
      // 记录初始x位置
      const clientX = e.clientX;
      // 鼠标按下，计算当前元素距离可视区的距离
      const disX = e.clientX - resizeEl.offsetLeft;
      const disY = e.clientY - resizeEl.offsetTop;
      document.onmousemove = function (e) {
        e.preventDefault(); // 移动时禁用默认事件
        // 通过事件委托，计算移动的距离
        const x = e.clientX - disX + (e.clientX - clientX);//这里 由于elementUI的dialog控制居中的，所以水平拉伸效果是双倍
        const y = e.clientY - disY;
        //比较是否小于最小宽高
        dragDom.style.width = x > minWidth ? `${x}px` : minWidth + 'px';
        dragDom.style.height = y > minHeight ? `${y}px` : minHeight + 'px';
        if (!hasSetBodyHight) {
          let footerHeight = dragDom.querySelector('.el-dialog__footer') && dragDom.querySelector('.el-dialog__footer').offsetHeight;
          dragDom.querySelector('.el-dialog__body').style.height = 'calc(100% - ' + (dialogHeaderEl.offsetHeight + footerHeight) + 'px)';
          hasSetBodyHight = true;
        }
      };
      //拉伸结束
      document.onmouseup = function (e) {
        document.onmousemove = null;
        document.onmouseup = null;
        el.dispatchEvent(resizeEvent);
      };
    }
  }
}

使用 的时候 在main.js里面全局注册

import elDragDialog from '@/directive/el-drag-dialog' // 引入移动事件（el-drag-dialog.js的内容为上面的代码块）
Vue.directive('el-drag-dialog', elDragDialog);//添加标签事件绑定 可以放大移动弹窗
//弹窗默认点击遮罩改为不关闭 为了防止和拖拽冲突 ，这句需要放在use ElementUI之前（也可以不加这句，自己测试区别）
ElementUI.Dialog.props.closeOnClickModal.default = false;

全局注册成功后在需要加上此事件的弹窗加上el-drag-dialog属性即可

 <el-dialog v-el-drag-dialog width="80%" :visible.sync="dialogFormVisible">
          测试弹窗内容
    </el-dialog>