HTML Attributes for <INPUT ...>
onKeyUp ="script command(s)"
onKeyDown ="script command(s)"

See also
onKeyDown is triggered when the user presses down on a key while the cursor is in the input field. onKeyUp is triggered when the the key goes up again. For example, the following code puts "down!" in the status bar when the key goes down, and "up!" when the key goes up:

This Code Makes This 
<INPUT 
 NAME="realname" 
 onKeyDown="window.status='down!'"
 onKeyUp="window.status='up!'">
(Form is not live)

onKeyDown and onKeyUp represent the component actions of pressing a key. They cannot be cancelled. In most situations where you might consider using onKeyDown or onKeyUp you will probably find that onKeyPress is more useful. onKeyPress represents the entire keystroke and can cancel the keystroke.

<INPUT AUTOCOMPLETE="..."> >