Drag and Drop script with custom events

dragAndDrop.js

var DragDrop = function() {
    var dragdrop = new EventTarget(),
        dragging = null,
        diffX = 0,
        diffY = 0;
        
    function handleEvent(event) {
        event = EventUtil.getEvent(event);
        var target = EventUtil.getTarget(event);
        
        switch(event.type) {
            case "mousedown":
                if (target.className.indexOf("draggable") > -1) {
                    dragging = target;
                    diffX = event.clientX - target.offsetLeft;
                    diffY = event.clientY = target.offsetTop;
                    dragdrop.fire({
                        type: "dragstart",
                        target: dragging,
                        x: event.clientX,
                        y: event.clientY
                    });
                }
                break;
                
            case "mousemove":
                if (dragging !== null) {
                    dragging.style.left = (event.clientX - diffX) + "px";
                    draggin.style.top = (event.clientY - diffY) + "px";
                    dragdrop.fire({
                        type: "drag",
                        target: dragging,
                        x: event.clientX,
                        y: event.clientY
                    });
                }
                break;
                
            case "mouseup":
                dragdrop.fire({
                    type: "dragend",
                    target: dragging,
                    x: event.clientX,
                    y: event.clientY
                });
                dragging = null;
                break;
        }
    }
    
    dragdrop.enable = function() {
        Event.Util.addHandler(document, "mousedown", handleEvent);
        Event.Util.addHandler(document, "mousemove", handleEvent);
        Event.Util.addHandler(document, "mouseup", handleEvent);
    };
    
    dragdrop.disable = function() {
        Event.Util.removeHandler(document, "mousedown", handleEvent);
        Event.Util.removeHandler(document, "mousemove", handleEvent);
        Event.Util.removeHandler(document, "mouseup", handleEvent);
    };
    
    return dragdrop;
}();