有時候用 jQuery 使用 event 物件時，會發現有些特殊事件的 property 抓不到 (undefined)
例如
mousewheel --> event.wheelDelta 
drop --> event.dataTransfer
touchstart --> event.touches[0].pageX
原因是 jQuery 的 event 只會包裝一般的屬性，特別的屬性要使用 event.originalEvent 去抓
event.originalEvent 是瀏覽器原生的 event

It's also important to note that the event object contains a property called originalEvent, which is the event object that the browser itself created. jQuery wraps this native event object with some useful methods and properties, but in some instances, you'll need to access the original event via event.originalEvent for instance. This is especially useful for touch events on mobile devices and tablets.

所以開發時當有些特殊屬性抓不到時，可以考慮用 event.originalEvent 去抓看看

    // 這是用滾輪放大縮小圖片 (此範例firefox不支援)

    $("#imgProductBig").bind("mousewheel", function (ev) {

        var delta = ev.originalEvent.wheelDelta > 0 ? 1 : -1;

        if (delta > 0 && zoomValue < 150) {

            zoomValue += 10;

        }

        else if (delta < 0 && zoomValue > 50) {

            zoomValue -= 10;

        }

        $(this).css("zoom", zoomValue + '%');

        return false;

    });