JavaScript实现拖拽简单效果

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
        }

//屏幕的高度
// var h=document.documentElement.clientHeight
// var w=document.documentElement.clientWidth;


// console.log(h,w);

<div class="one">
​
    </div>
    <div class="two"></div>
    <script>
        var o = document.querySelector('.one');
        var ox = document.querySelector('.two');
​
        //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;
            //计算最大左边距和上边距(边界)
            var maxLeft = document.documentElement.clientWidth - this.offsetWidth;
            var maxTop = document.documentElement.clientHeight - this.offsetHeight;
            //碰撞
            var L2 = ox.offsetLeft;
            var T2 = ox.offsetTop;
            var R2 = L2 + ox.offsetWidth;
            var B2 = T2 + ox.offsetHeight
            //鼠标移动
            document.onmousemove = function (e) {
                e = e || window.event
                var x = e.clientX - offsetX;
                var y = e.clientY - offsetY;
​
                //计算边界
                if (x <= 0) x = 0
                if (y <= 0) y = 0
                if (x >= maxLeft) x = maxLeft;
                if (y >= maxTop) y = maxTop;
​
                o.style.left = x + "px";
                o.style.top = y + "px";
                //计算碰撞
                var L1 = o.offsetLeft;
                var T1 = o.offsetTop;
                var R1 = L1 + o.offsetWidth;
                var B1 = T1 + o.offsetHeight;
                if (L1 > R2 || T1 > B2 || R1 < L2 || B1 < T2) {   //不碰撞
                    ox.style.backgroundColor = "blue"
                } else {
                    ox.style.backgroundColor = "orange"
                }
            }
            //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
        }
​
</script>