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;
      };
    } 
  }
})

document.body.clientWidth //BODY对象宽度
document.body.clientHeight //BODY对象高度
document.documentElement.clientWidth //可见区域宽度
document.documentElement.clientHeight //可见区域高度

// 引入Dialog可拖拽，注意文件所在目录。目前尚未发现引入的先后关系，若有再补充
import './directives.js';

<el-dialog v-dialogDrag></el-dialog>