JavaScript Drag and Drop

<script type="text/javascript">

var dragElement = 'dragobject'  // this is the id of the element you wish to drag
var dropElement = 'dropobject'  // this is the id of the element you wish to drop objects onto

var dragObject = null;
var numtasks = document.tasks.elements.length;
var DRAG_lastX, DRAG_lastY;
var DRAG_startX, DRAG_startY;

document.onmousemove = mouseMove;
document.onmouseup = mouseUp;
document.onselectstart = function () { return false; }
for (var i = 0; i < numtasks; i++) {
        document.getElementById(dragElement).onmousedown = function() {                           
                dragObject = this;                
                dragObject.style.position = 'absolute';
                DRAG_lastX = 0;
                DRAG_lastY = 0;
                DRAG_startX = dragObject.style.left;
                DRAG_startY = dragObject.style.top;
                }
    }
}

function mouseMove(ev){
    ev = ev || window.event;
    var x = ev.pageX ? ev.pageX : ev.x;
    var y = ev.pageY ? ev.pageY : ev.y;
   
    if (dragObject != null) {
      DRAG_lastX = x + 1;
      DRAG_lastY = y + 1;
      dragObject.style.left = DRAG_lastX.toString() + 'px';
      dragObject.style.top = DRAG_lastY.toString() + 'px';
    }
}

function mouseUp(ev){
    ev = ev || window.event;
    var theTarget = ev.target ? ev.target : ev.srcElement;

    if (theTarget.id == dropElement) {
        alert('Item Dropped');
    }
    else {
        dragObject.style.left = DRAG_startX;
        dragObject.style.top = DRAG_startY;
    }

    dragObject   = null;
}

</script>