KeyboardEvent.keyCode - Web APIs 编辑

Deprecated

This feature is no longer recommended. Though some browsers might still support it, it may have already been removed from the relevant web standards, may be in the process of being dropped, or may only be kept for compatibility purposes. Avoid using it, and update existing code if possible; see the compatibility table at the bottom of this page to guide your decision. Be aware that this feature may cease to work at any time.

The deprecated KeyboardEvent.keyCode read-only property represents a system and implementation dependent numerical code identifying the unmodified value of the pressed key. This is usually the decimal ASCII (RFC 20) or Windows 1252 code corresponding to the key. If the key can't be identified, this value is 0.

You should avoid using this if possible; it's been deprecated for some time. Instead, you should use KeyboardEvent.code, if it's implemented. Unfortunately, some browsers still don't have it, so you'll have to be careful to make sure you use one which is supported on all target browsers.

Web developers shouldn't use the keyCode attribute for printable characters when handling keydown and keyup events. As described above, the keyCode attribute is not useful for printable characters, especially those input with the Shift or Alt key pressed. When implementing a shortcut key handler, the keypress event is usually better (at least when Gecko is the runtime in use). See Gecko Keypress Event for details.

Example

window.addEventListener("keydown", function (event) {
  if (event.defaultPrevented) {
    return; // Should do nothing if the default action has been cancelled
  }

  var handled = false;
  if (event.key !== undefined) {
    // Handle the event with KeyboardEvent.key and set handled true.
  } else if (event.keyCode !== undefined) {
    // Handle the event with KeyboardEvent.keyCode and set handled true.
  }

  if (handled) {
    // Suppress "double action" if event handled
    event.preventDefault();
  }
}, true);

Specifications

Browser compatibility

BCD tables only load in the browser

Value of keyCode

Printable keys in standard position

The value of key events which are caused by pressing or releasing printable keys in standard position is not compatible between browsers.

IE just exposes the native virtual keycode value as KeyboardEvent.keyCode.

Google Chrome, Chromium and Safari must decide the value from the input character. If the inputting character can be inputted with the US keyboard layout, they use the keyCode value on the US keyboard layout.

Starting in Firefox 15 (Firefox 15.0 / Thunderbird 15.0 / SeaMonkey 2.12), Gecko gets keyCode values from ASCII characters inputtable by the key — even with shift modifiers or an ASCII capable keyboard layout. See the following rules for details:

1. If the system is Windows and the native keycode of the pressed key indicates that the key is a-z or 0-9, use a keycode for it.
2. If the system is Mac and the native keycode of the pressed key indicates that the key is 0-9, use a keycode for it.
3. If the pressed key inputs an ASCII alphabetic or numeric character with no modifier key, use a keycode for it.
4. If the pressed key inputs an ASCII alphabetic or numeric character with a Shift key modifier, use a keycode for it.
5. If the pressed key inputs a different ASCII character with no modifier key, use a keycode for it.
6. If the pressed key inputs a different ASCII character with a Shift key modifier, use a keycode for it.
7. Otherwise, i.e., pressed key inputs a unicode character:
   1. If the keyboard layout is ASCII-capable (i.e., can input ASCII alphabets), use 0 or compute with the following additional rules.
   2. Otherwise, i.e., the keyboard layout isn't ASCII capable, use the ASCII capable keyboard layout installed on the environment with the highest priority:
      1. If the pressed key on the alternative keyboard layout inputs an ASCII alphabetic or numeric character, use a keycode for it.
      2. Otherwise, use 0 or compute with the following additional rules.

Starting in Firefox 60 (Firefox 60.0 / Thunderbird 60.0 / SeaMonkey 2.57), Gecko sets keyCode values of punctuation keys as far as possible (when points 7.1 or 7.2 in the above list are reached) with the following rules:

The purpose of these new additional rules is for making users whose keyboard layouts map unicode characters to punctuation keys in a US keyboard layout can use web applications which support Firefox only with ASCII-capable keyboard layouts or just with a US keyboard layout. Otherwise, the newly mapped keyCode values may be conflict with other keys. For example, if the active keyboard layout is Russian, the keyCode value of both the "Period" key and "Slash" key are 190 (KeyEvent.DOM_VK_PERIOD). If you need to distinguish those keys but you don't want to support all keyboard layouts in the world by yourself, you should probably use KeyboardEvent.code.

1. If running macOS or Linux:
   1. If the active keyboard layout is not ASCII-capable and an alternative ASCII-capable keyboard layout is available.
      1. If the alternative ASCII-capable keyboard layout produces an ASCII character via just the unmodified key, use a keyCode for the character.
      2. If the alternative ASCII-capable keyboard layout produces an ASCII character with a Shift key modifier, use a keyCode for the shifted character.
      3. Otherwise, use a keyCode for an ASCII character produced by the key when the US keyboard layout is active.
   2. Otherwise, use a keyCode for an ASCII character produced by the key when the US keyboard layout is active.
2. If running on Windows:
   1. Use a keyCode value for an ASCII character produced by a key which is mapped to the same virtual keycode of Windows when the US keyboard layout is active.

*1 The value is input from JIS keyboard. When you use ANSI keyboard, the keyCode value and inputted character are what you select from the US keyboard layout.

*2 The key is a dead key. The value of keyup event is 0xBA (186).

*3 The key is a dead key. The value of keyup event is 0x10 (16).

*4 No key events are fired.

*5 The key isn't available with Greek keyboard layout (does not input any character). The value of keyup event is 0x00 (0).

Non-printable keys (function keys)

*1 On Windows, "AltGraph" key causes "ControlLeft" key event and "AltRight" key event.

*2 When Japanese keyboard layout is active, "CapsLock" key without Shift causes 0xF0 (240). The key works as "Alphanumeric" key whose label is "英数".

*3 When Japanese keyboard layout is active, "CapsLock" key without Shift causes 0x00 (0). The key works as "Alphanumeric" key whose label is "英数".

*1 keypress event is fired whose keyCode and charCode are 0x10 (16) but text isn't inputted into editor.

*2 On Mac, "Help" key is mapped to "Insert" key of PC keyboard. These keyCode values are the same as the "Insert" key's keyCode value.

*3 Tested on Fedora 20.

*4 Only keyup event is fired.

*5 PC's "PrintScreen", "ScrollLock" and "Pause" are mapped to Mac's "F13", "F14" and "F15". Chrome and Safari map same keyCode values with Mac's keys.

*6 "Pause" key with Control causes 0x03 (3).

*1 Tested on Fedora 20.

*2 PC's "PrintScreen", "ScrollLock" and "Pause" are mapped to Mac's "F13", "F14" and "F15". Firefox maps same keyCode values with PC's keys.

*3 Tested on Fedora 20. The keys don't cause GDK_Fxx keysyms. If the keys cause proper keysyms, these values must be same as IE.

*4 Tested on Fedora 20. The keys don't cause DOM key events on Chromium.

*5 keyUp event's keyCode value is 0x83 (131).

*6 Tested on Fedora 20. The keys don't cause DOM key events on Firefox.

*7 Only keydown event is fired.

*8 No DOM key events are fired on Firefox.

Numpad keys

*1 "NumLock" key works as "Clear" key on Mac.

* Recent Mac doesn't have "NumLock" key and state. Therefore, unlocked state isn't available.

Constants for keyCode value

Gecko defines a lot of keyCode values in KeyboardEvent for making the mapping table explicitly. These values are useful for add-on developers of Firefox, but not so useful in public web pages.

OEM specific keys on Windows

On Windows, some values of virtual keycode are defined (reserved) for OEM specific key. They are available for special keys on non-standard keyboard. In other words, some values are used for different meaning by two or more vendors (or hardware).

Starting Gecko 21 (and older than 15), OEM specific key values are available on the keyCode attribute only on Windows. So they are not useful for usual web applications. They are useful only for intranet applications or in similar situations.

See "Manufacturer-specific Virtual-Key Codes (Windows CE 5.0)" in MSDN for the detail.