js实现简单的拖拽效果

var o = document.querySelector('div');
 
        //鼠标按下
        o.onmousedown = function (e) {
            //鼠标相对于盒子的位置
            var offsetX = e.clientX - o.offsetLeft;
            var offsetY = e.clientY - o.offsetTop;
            //鼠标移动
            document.onmousemove = function (e) {
                o.style.left = e.clientX - offsetX + "px";
                o.style.top = e.clientY - offsetY + "px";
            }
            //鼠标抬起
            document.onmouseup = function () {
                document.onmousemove = null;
                document.onmouseup = null;
            }
        }

<button>btn1</button>
    <button>btn2</button>
    <script>
        var bts = document.querySelectorAll('button')
 
        bts[0].onclick = function () {
            console.log(1);
        }
        bts[1].onclick = function () {
            console.log(2);
        }
 
        // bts[0].setCapture()  //添加全局捕获
        // bts[0].releaseCapture() ;//释放全局捕获
</script>

var o = document.querySelector('div');
 
        //鼠标按下
        o.onmousedown = function (e) {
            if (o.setCapture) {   //IE低版本
                o.setCapture()
            }
            e = e || window.event
            //鼠标相对于盒子的位置
            var offsetX = e.clientX - o.offsetLeft;
            var offsetY = e.clientY - o.offsetTop;
            //鼠标移动
            document.onmousemove = function (e) {
                e = e || window.event
                o.style.left = e.clientX - offsetX + "px";
                o.style.top = e.clientY - offsetY + "px";
            }
            //鼠标抬起
            document.onmouseup = function () {
                document.onmousemove = null;
                document.onmouseup = null;
                if (o.releaseCapture) {
                    o.releaseCapture();//释放全局捕获   
                }
            }
            return false;//标准浏览器的默认行为
        }