keycode cross-reference table

1. The keyCode is a numerical value associated with a specific keyboard key, provided by the browser when a keyboard event occurs.

2. When a user presses a key on the keyboard, JavaScript can access this key code through the event object to determine which key was pressed.

3. Key codes are typically used in the following JavaScript events:

(1) keydown event: Triggered when the user presses any key on the keyboard.

(2) `keyup` event: Triggered when the user releases a key on the keyboard.

4. Keycode limitations: Keycodes are case-insensitive, not limited by keyboard layout, and function keys do not generate keycodes.

5. Key codes may be deprecated in the future; alternative solutions should be used when working with key codes.