html

<style>
    #app{
        position: relative;     /*定位*/
        top: 10px;
        left: 10px;
        width: 200px;
        height: 200px;
        background: #666;       /*设置一下背景*/
    }
</style>
<body>
    <div id="app" @mousedown="move">       <!--绑定按下事件-->
        {{positionX}}
        {{positionY}}
    </div>
</body>

JS

//main.js
let app = new Vue({
    el:'#app',
    data:{
        positionX:0,
        positionY:0,
    },
    methods:{
        move(e){
            let odiv = e.target;        //获取目标元素
            
            //算出鼠标相对元素的位置
            let disX = e.clientX - odiv.offsetLeft;
            let disY = e.clientY - odiv.offsetTop;
            document.onmousemove = (e)=>{       //鼠标按下并移动的事件
                //用鼠标的位置减去鼠标相对元素的位置，得到元素的位置
                let left = e.clientX - disX;    
                let top = e.clientY - disY;
                
                //绑定元素位置到positionX和positionY上面
                this.positionX = top;
                this.positionY = left;
                
                //移动当前元素
                odiv.style.left = left + 'px';
                odiv.style.top = top + 'px';
            };
            document.onmouseup = (e) => {
                document.onmousemove = null;
                document.onmouseup = null;
            };
        }    
    
    },
    computed:{},
});

指令形式

//main.js

let app = new Vue({
    el:'#app',
    data:{},
    methods:{},
    directives: {
        drag: {
            // 指令的定义
            bind: function (el) {
                let odiv = el;   //获取当前元素
                oDiv.onmousedown = (e) => {
                    //算出鼠标相对元素的位置
                    let disX = e.clientX - odiv.offsetLeft;
                    let disY = e.clientY - odiv.offsetTop;
                    
                    document.onmousemove = (e)=>{
                        //用鼠标的位置减去鼠标相对元素的位置，得到元素的位置
                        let left = e.clientX - disX;    
                        let top = e.clientY - disY;
                      
                        //绑定元素位置到positionX和positionY上面
                        this.positionX = top;
                        this.positionY = left;
                
                        //移动当前元素
                        odiv.style.left = left + 'px';
                        odiv.style.top = top + 'px';
                    };
                    document.onmouseup = (e) => {
                        document.onmousemove = null;
                        document.onmouseup = null;
                    };
                };
            }
        }
    }
});