el-dialog实现可拖拽

Vue Directive申明：

Vue.directive('dragglable', {
    bind(el) {
        // 获取弹窗头部元素
        const dialogHeaderEl = el.querySelector(".el-dialog__header");
        // 获取整个弹窗元素
        const dragDom = el.querySelector(".el-dialog");
        dialogHeaderEl.style.cursor = "move";
        dialogHeaderEl.onmousedown = (e) => {
            // 计算鼠标相对弹窗头部的偏移量
            const disX = e.clientX - dialogHeaderEl.offsetLeft;
            const disY = e.clientY - dialogHeaderEl.offsetTop;
            // 获取可视区域的宽高
            const screenWidth = document.body.clientWidth;
            const screenHeight = document.body.clientHeight;
            const dragDomWidth = dragDom.offsetWidth;
            const dragDomHeight = dragDom.offsetHeight;
            // 计算可移动范围的边界值
            const minDragDomLeft = dragDom.offsetLeft;
            const maxDragDomLeft = screenWidth - dragDom.offsetLeft - dragDomWidth;
            const minDragDomTop = dragDom.offsetTop;
            const maxDragDomTop = screenHeight - dragDom.offsetTop - dragDomHeight;
            // 用于存储弹窗的位置信息
            let styL,
            styT;
            if (window.getComputedStyle(dragDom).left.includes("%")) {
                styL = +document.body.clientWidth * ( + window.getComputedStyle(dragDom).left.replace(/%/g, "") / 100);
                styT = +document.body.clientHeight * ( + window.getComputedStyle(dragDom).top.replace(/%/g, "") / 100);
            } else {
                styL = +window.getComputedStyle(dragDom).left.replace(/px/g, "");
                styT = +window.getComputedStyle(dragDom).top.replace(/px/g, "");
            }
            document.onmousemove = function(e) {
                let left = e.clientX - disX;
                let top = e.clientY - disY;
                if ( - left > minDragDomLeft) {
                    left = -minDragDomLeft;
                } else if (left > maxDragDomLeft) {
                    left = maxDragDomLeft;
                }
                if ( - top > minDragDomTop) {
                    top = -minDragDomTop;
                } else if (top > maxDragDomTop) {
                    top = maxDragDomTop;
                }
                dragDom.style.cssText += `;left: ${ left + styL }px;top: ${ top + styT }px;`;
            };
            // 清除鼠标移动和松开事件的监听 
            document.onmouseup = function() {
                document.onmousemove = null;
                document.onmouseup = null;
            };
        };
    }
});