KeyboardEvent - Web APIs 编辑

KeyboardEvent objects describe a user interaction with the keyboard; each event describes a single interaction between the user and a key (or combination of a key with modifier keys) on the keyboard. The event type (keydown, keypress, or keyup) identifies what kind of keyboard activity occurred.

Note: KeyboardEvent events just indicate what interaction the user had with a key on the keyboard at a low level, providing no contextual meaning to that interaction. When you need to handle text input, use the input event instead. Keyboard events may not be fired if the user is using an alternate means of entering text, such as a handwriting system on a tablet or graphics tablet.

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Constructor

KeyboardEvent()

Creates a new KeyboardEvent object.

Constants

The KeyboardEvent interface defines the following constants.

Keyboard locations

The following constants identify which part of the keyboard the key event originates from. They are accessed as KeyboardEvent.DOM_KEY_LOCATION_STANDARD and so forth.

Keyboard location identifiers

Constant	Value	Description
DOM_KEY_LOCATION_STANDARD	0x00	The key described by the event is not identified as being located in a particular area of the keyboard; it is not located on the numeric keypad (unless it's the NumLock key), and for keys that are duplicated on the left and right sides of the keyboard, the key is, for whatever reason, not to be associated with that location. Examples include alphanumeric keys on the standard PC 101 US keyboard, the NumLock key, and the space bar.
DOM_KEY_LOCATION_LEFT	0x01	The key is one which may exist in multiple locations on the keyboard and, in this instance, is on the left side of the keyboard. Examples include the left Control key, the left Command key on a Macintosh keyboard, or the left Shift key.
DOM_KEY_LOCATION_RIGHT	0x02	The key is one which may exist in multiple positions on the keyboard and, in this case, is located on the right side of the keyboard. Examples include the right Shift key and the right Alt key (Option on a Mac keyboard).
DOM_KEY_LOCATION_NUMPAD	0x03	The key is located on the numeric keypad, or is a virtual key associated with the numeric keypad if there's more than one place the key could originate from. The NumLock key does not fall into this group and is always encoded with the location DOM_KEY_LOCATION_STANDARD. Examples include the digits on the numeric keypad, the keypad's Enter key, and the decimal point on the keypad.

Properties

This interface also inherits properties of its parents, UIEvent and Event.

KeyboardEvent.altKey Read only

Returns a Boolean that is true if the Alt ( Option or ⌥ on OS X) key was active when the key event was generated.

KeyboardEvent.code Read only

Returns a DOMString with the code value of the physical key represented by the event. Warning: This ignores the user's keyboard layout, so that if the user presses the key at the "Y" position in a QWERTY keyboard layout (near the middle of the row above the home row), this will always return "KeyY", even if the user has a QWERTZ keyboard (which would mean the user expects a "Z" and all the other properties would indicate a "Z") or a Dvorak keyboard layout (where the user would expect an "F").

KeyboardEvent.ctrlKey Read only

Returns a Boolean that is true if the Ctrl key was active when the key event was generated.

KeyboardEvent.isComposing Read only

Returns a Boolean that is true if the event is fired between after compositionstart and before compositionend.

KeyboardEvent.key Read only

Returns a DOMString representing the key value of the key represented by the event.

KeyboardEvent.locale Read only

Returns a DOMString representing a locale string indicating the locale the keyboard is configured for. This may be the empty string if the browser or device doesn't know the keyboard's locale. Note: This does not describe the locale of the data being entered. A user may be using one keyboard layout while typing text in a different language.

KeyboardEvent.location Read only

Returns a Number representing the location of the key on the keyboard or other input device. A list of the constants identifying the locations is shown above in Keyboard locations.

KeyboardEvent.metaKey Read only

Returns a Boolean that is true if the Meta key (on Mac keyboards, the ⌘ Command key; on Windows keyboards, the Windows key (⊞)) was active when the key event was generated.

KeyboardEvent.repeat Read only

Returns a Boolean that is true if the key is being held down such that it is automatically repeating.

KeyboardEvent.shiftKey Read only

Returns a Boolean that is true if the Shift key was active when the key event was generated.

Methods

This interface also inherits methods of its parents, UIEvent and Event.

KeyboardEvent.getModifierState()

Returns a Boolean indicating if a modifier key such as Alt, Shift, Ctrl, or Meta, was pressed when the event was created.

Obsolete methods

KeyboardEvent.initKeyEvent()

Initializes a KeyboardEvent object. This was implemented only by Firefox, and is no longer supported even there; instead, you should use the KeyboardEvent() constructor.

KeyboardEvent.initKeyboardEvent()

Initializes a KeyboardEvent object. This is now deprecated. You should instead use the KeyboardEvent() constructor.

Obsolete properties

KeyboardEvent.char Read only

Returns a DOMString representing the character value of the key. If the key corresponds to a printable character, this value is a non-empty Unicode string containing that character. If the key doesn't have a printable representation, this is an empty string. Note: If the key is used as a macro that inserts multiple characters, this attribute's value is the entire string, not just the first character.

KeyboardEvent.charCode Read only

Returns a Number representing the Unicode reference number of the key; this attribute is used only by the keypress event. For keys whose char attribute contains multiple characters, this is the Unicode value of the first character in that attribute. In Firefox 26 this returns codes for printable characters. Warning: This attribute is deprecated; you should use KeyboardEvent.key instead, if available.

KeyboardEvent.keyCode Read only

Returns a Number representing a system and implementation dependent numerical code identifying the unmodified value of the pressed key. Warning: This attribute is deprecated; you should use KeyboardEvent.key instead, if available.

KeyboardEvent.keyIdentifier Read only

This property is non-standard and has been deprecated in favor of KeyboardEvent.key. It was part of an old version of DOM Level 3 Events.

KeyboardEvent.keyLocation Read only

This is a non-standard deprecated alias for KeyboardEvent.location. It was part of an old version of DOM Level 3 Events.

KeyboardEvent.which Read only

Returns a Number representing a system and implementation dependent numeric code identifying the unmodified value of the pressed key; this is usually the same as keyCode. Warning: This attribute is deprecated; you should use KeyboardEvent.key instead, if available.

Events

The following events are based on the KeyboardEvent type. They can be delivered to any object which implements GlobalEventHandlers, including Element, Document, and Window. In the list below, each event links to the documentation for the Document handler for the event, which applies generally to all of the recipients.

keydown

A key has been pressed.

keyup

A key has been released.

Obsolete events

keypress

A key that normally produces a character value has been pressed. This event was highly device-dependent and is obsolete. You should not use it.

Usage notes

There are three types of keyboard events: keydown, keypress, and keyup. For most keys, Gecko dispatches a sequence of key events like this:

1. When the key is first pressed, the keydown event is sent.
2. If the key is not a modifier key, the keypress event is sent.
3. When the user releases the key, the keyup event is sent.

Special cases

Some keys toggle the state of an indicator light; these include keys such as Caps Lock, Num Lock, and Scroll Lock. On Windows and Linux, these keys dispatch only the keydown and keyup events.

On Linux, Firefox 12 and earlier also dispatched the keypress event for these keys.

However, a limitation of the macOS event model causes Caps Lock to dispatch only the keydown event. Num Lock was supported on some older laptop models (2007 models and older), but since then, macOS hasn't supported Num Lock even on external keyboards. On older MacBooks with a Num Lock key, that key doesn't generate any key events. Gecko does support the Scroll Lock key if an external keyboard which has an F14 key is connected. In certain older versions of Firefox, this key generated a keypress event; this inconsistent behavior was bug 602812.

Auto-repeat handling

When a key is pressed and held down, it begins to auto-repeat. This results in a sequence of events similar to the following being dispatched:

1. keydown
2. keypress
3. keydown
4. keypress
5. <<repeating until the user releases the key>>
6. keyup

This is what the DOM Level 3 specification says should happen. There are some caveats, however, as described below.

Auto-repeat on some GTK environments such as Ubuntu 9.4

In some GTK-based environments, auto-repeat dispatches a native key-up event automatically during auto-repeat, and there's no way for Gecko to know the difference between a repeated series of keypresses and an auto-repeat. On those platforms, then, an auto-repeat key will generate the following sequence of events:

1. keydown
2. keypress
3. keyup
4. keydown
5. keypress
6. keyup
7. <<repeating until the user releases the key>>
8. keyup

In these environments, unfortunately, there's no way for web content to tell the difference between auto-repeating keys and keys that are just being pressed repeatedly.

Auto-repeat handling prior to Gecko 5.0

Before Gecko 5.0 (Firefox 5.0 / Thunderbird 5.0 / SeaMonkey 2.2), keyboard handling was less consistent across platforms.

Windows

Auto-repeat behavior is the same as in Gecko 4.0 and later.

Mac

After the initial keydown event, only keypress events are sent until the keyup event occurs; the inter-spaced keydown events are not sent.

Linux

The event behavior depends on the specific platform. It will either behave like Windows or Mac depending on what the native event model does.

Note: Manually firing an event does not generate the default action associated with that event. For example, manually firing a key event does not cause that letter to appear in a focused text input. In the case of UI events, this is important for security reasons, as it prevents scripts from simulating user actions that interact with the browser itself.

Example

<!DOCTYPE html>
<html>
<head>
<script>
'use strict';

document.addEventListener('keydown', (event) => {
  const keyName = event.key;

  if (keyName === 'Control') {
    // do not alert when only Control key is pressed.
    return;
  }

  if (event.ctrlKey) {
    // Even though event.key is not 'Control' (e.g., 'a' is pressed),
    // event.ctrlKey may be true if Ctrl key is pressed at the same time.
    alert(`Combination of ctrlKey + ${keyName}`);
  } else {
    alert(`Key pressed ${keyName}`);
  }
}, false);

document.addEventListener('keyup', (event) => {
  const keyName = event.key;

  // As the user releases the Ctrl key, the key is no longer active,
  // so event.ctrlKey is false.
  if (keyName === 'Control') {
    alert('Control key was released');
  }
}, false);

</script>
</head>

<body>
</body>
</html>

Specifications

Specification	Status	Comment
UI Events The definition of 'KeyboardEvent' in that specification.	Working Draft

The KeyboardEvent interface specification went through numerous draft versions, first under DOM Events Level 2 where it was dropped as no consensus arose, then under DOM Events Level 3. This led to the implementation of non-standard initialization methods, the early DOM Events Level 2 version, KeyboardEvent.initKeyEvent() by Gecko browsers and the early DOM Events Level 3 version, KeyboardEvent.initKeyboardEvent() by others. Both have been superseded by the modern usage of a constructor: KeyboardEvent().

Browser compatibility

BCD tables only load in the browser

Compatibility notes

• As of Firefox 65, the keypress event is no longer fired for non-printable keys (bug 968056), except for the Enter key, and the Shift + Enter and Ctrl + Enter key combinations (these were kept for cross-browser compatibility purposes).

See also

• KeyboardEvent.code.
• KeyboardEvent.key.
• KeyboardEvent.getModifierState()