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.
Event.srcElement is a proprietary alias for the standard
Event.target property. It is specific to old versions of Microsoft Internet Explorer.
Not part of any specification.
Microsoft has a description on MSDN.
|Feature||Chrome||Edge||Firefox (Gecko)||Internet Explorer||Opera||Safari|
|Basic support||(Yes)||(Yes)||No support ||(Yes)||(Yes)||(Yes)|
|Feature||Android||Edge||Firefox Mobile (Gecko)||IE Mobile||Opera Mobile||Safari Mobile|
|Basic support||?||(Yes)||No support ||?||?||?|
: bug 453968