CORE ATTRIBUTE:  onkeydown
onkeydown="action"
Available in versions: 4.0
HTML 4.0 tag compatibility: All tags except applet, base, basefront, bdo, br, font, frame, frameset, head, html, iframe, isindex, meta, param, script, style, title
 
The onkeydown core attribute is an event handler that is associated with pressing down a key on the keyboard while the mouse is inside a selected HTML tag (element). In other words, the key down event occurred while the HTML element was in focus. Whenever you press down the key, the script code of the onkeydown is executed. This script can also call functions or subroutines which contain code that you want to run when this event occurs. For example, if you only want numbers to be entered, you could capture the value of the key and take appropriate action if a non-numeric key was pressed.
 
The similar onkeyup core attribute is an event handler that is associated with the release of a key after it was pressed down, and the onkeypress core attribute is an event handler that is associated with the pressing of a key.
 
In this example, place the mouse inside the textarea element and type in a word. Every time you press a key down, one line of JavaScript code is executed which causes an alert box to be displayed with a message. Note how the alert comes up before the character is displayed inside the textarea.
 
Code:
<textarea onkeydown="javascript: alert('A key was pressed down')">
</textarea>
 
Output:

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