实现一：vue3+vueuse

/*
	需求：实现一个拖拽指令，可在父元素区域任意拖拽元素。

	思路：
		1、设置需要拖拽的元素为absolute，其父元素为relative。
		2、鼠标按下(onmousedown)时记录目标元素当前的 left 和 top 值。
		3、鼠标移动(onmousemove)时计算每次移动的横向距离和纵向距离的变化值，并改变元素的 left 和 top 值
		4、鼠标松开(onmouseup)时完成一次拖拽

	使用：在 Dom 上加上 v-draggable 即可
	<div class="dialog-model" v-draggable></div>
*/
import type { Directive } from "vue";
interface ElType extends HTMLElement {
	parentNode: any;
}
const draggable: Directive = {
	mounted: function (el: ElType) {
		el.style.cursor = "move";
		el.style.position = "absolute";
		el.onmousedown = function (e) {
			let disX = e.pageX - el.offsetLeft;
			let disY = e.pageY - el.offsetTop;
			document.onmousemove = function (e) {
				let x = e.pageX - disX;
				let y = e.pageY - disY;
				let maxX = el.parentNode.offsetWidth - el.offsetWidth;
				let maxY = el.parentNode.offsetHeight - el.offsetHeight;
				if (x < 0) {
					x = 0;
				} else if (x > maxX) {
					x = maxX;
				}

				if (y < 0) {
					y = 0;
				} else if (y > maxY) {
					y = maxY;
				}
				el.style.left = x + "px";
				el.style.top = y + "px";
			};
			document.onmouseup = function () {
				document.onmousemove = document.onmouseup = null;
			};
		};
	}
};
export default draggable;

<template>
	<div class="card content-box">
		<div v-draggable class="drag-box flx-center">点击拖拽哦~</div>
	</div>
</template>

<script setup lang="ts" name="dragDirect"></script>

<style scoped lang="scss">
.content-box {
	position: relative;
	width:100%;
	height:100%;
	.drag-box {
		position: absolute;
		top: 110px;
		width: 300px;
		height: 300px;
		font-size: 23px;
		font-weight: bold;
		color: var(--el-color-primary-light-3);
		background: var(--el-color-primary-light-9);
		border-radius: 50%;
		display: flex;
		align-items: center;
		justify-content: center;
	}
}

</style>

vue2实现：

1、在main.js同级建一个文件directives.js

import Vue from 'vue';

// v-dialogDrag: 弹窗拖拽
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';

    // 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);

    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;

      // 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;
      };
    }
  }
})

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

    el.onmousedown = (e) => {

      // 鼠标按下，计算当前元素距离可视区的距离
      const disX = e.clientX - el.offsetLeft;

      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 l = e.clientX - disX;
        dragDom.style.width = `${l}px`;
      };

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

2、main.js添加引用

import './directives.js'

3、在需要用到拖拽功能的弹窗标签上加 

v-dialogDrag

例如：

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

即可