v-dialogDrag: 弹窗拖拽指令，控制el-dialog拖拽

// 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;
          };
        }
      }
})