DOM events don't have the “on” prefix

One of the very common mistakes when switching from traditional object-property-based event registration (window.onload = handler) to DOM event registration (window.addEventListener('load',handler)) is the reuse of object property as the event name. The “on” property prefix should not be part of the event name (for example, use load instead of onload and mouseover instead of onmouseover).

To make matters worse, the attachEvent method (Microsoft equivalent of the addEventListener DOM method) expects the event names with the “on” prefix.