js to achieve simple drag effect

var o = document.querySelector('div');
 
        //Mouse down o.onmousedown = function (e) {
            //Mouse position relative to the box var offsetX = e.clientX - o.offsetLeft;
            var offsetY = e.clientY - o.offsetTop;
            //Mouse movement document.onmousemove = function (e) {
                o.style.left = e.clientX - offsetX + "px";
                o.style.top = e.clientY - offsetY + "px";
            }
            //Mouse up 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() //Add global capture // bts[0].releaseCapture() ; //Release global capture</script>

var o = document.querySelector('div');
 
        //Mouse down o.onmousedown = function (e) {
            if (o.setCapture) { //IE lower version o.setCapture()
            }
            e = e || window.event
            //Mouse position relative to the box var offsetX = e.clientX - o.offsetLeft;
            var offsetY = e.clientY - o.offsetTop;
            //Mouse movement document.onmousemove = function (e) {
                e = e || window.event
                o.style.left = e.clientX - offsetX + "px";
                o.style.top = e.clientY - offsetY + "px";
            }
            //Mouse up document.onmouseup = function () {
                document.onmousemove = null;
                document.onmouseup = null;
                if (o.releaseCapture) {
                    o.releaseCapture(); //Release global capture}
            }
            return false; //Default behavior of standard browsers}