You could implement this notification using a floating DIV section display during activity, or using a simple message on the browser's status bar (although this is considered bad form by some).

You can display output as octal, hex, decimal, floating point, ASCII with backslash escapes, or named characters (nl for newline, ht for horizontal TAB, etc.).

A popup window that can be used to display an arbitrary view. The popup Windows is a floating container that appears on top of the current activity.