This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.
window.event is a proprietary Microsoft Internet Explorer property which is only available while a DOM event handler is being called. Its value is the Event object currently being handled.
Not part of any specification.
Microsoft has a description on MSDN.
|Feature||Chrome||Edge||Firefox (Gecko)||Internet Explorer||Opera||Safari (WebKit)|
|Basic support||(Yes)||(Yes)||No support||(Yes)||?||?|
|Feature||Android||Edge||Firefox Mobile (Gecko)||IE Phone||Opera Mobile||Safari Mobile|