La propiedad de solo lectura KeyboardEvent.key
retorna el valor de la tecla presionada por el usuario while taking into considerations the state of modifier keys such as the shiftKey
as well as the keyboard locale/layout. Its value is determined as follows:
See a full list of key values.
- Si la tecla presionada tiene una representación impresa, el valor devuelto es una cadena de caracteres Unicode no-vacía que contiene la representación imprimible de la tecla.
- Si la tecla presionada es un control o un carácter especial, el valor devuelto es uno de los valores clave definidos.
- If the
KeyboardEvent
represents the press of a dead key, the key value must be "Dead
". - Some specialty keyboard keys (such as the extended keys for controlling media on multimedia keyboards) don't generate key codes on Windows; instead, they trigger
WM_APPCOMMAND
events. These events get mapped to DOM keyboard events, and are listed among the "Virtual key codes" for Windows, even though they aren't actually key codes. - If the key cannot be identified, the returned value is
"Unidentified"
.
KeyboardEvent Sequence
KeyboardEvent
s are fired in a pre-determined sequence and understanding this will go a long way into understanding the key
property value for a particular KeyboardEvent
. For a given key press, the sequence of KeyboardEvent
s fired is as follows assuming that Event.preventDefault
is not called:
- A
keydown
event is first fired. If the key is held down further and the key produces a character key, then the event continues to be emitted in a platform implementation dependent interval and theKeyboardEvent.repeat
read only property is set totrue
. - If the key produces a character key that would result in a character being inserted into possibly an
<input>
,<textarea>
or an element withHTMLElement.contentEditable
set to true, thebeforeinput
andinput
event types are fired in that order. Note that some other implementations may firekeypress
event if supported. The events will be fired repeatedly while the key is held down. - A
keyup
event is fired once the key is released. This completes the process.
In sequence 1 & 3, the KeyboardEvent.key
attribute is defined and is set appropriately to a value according to the rules defined ealier.
KeyboardEvent Sequence Sample
Consider the event sequence generated when we interact with the ShiftKey
and the legend key 2
using a U.S keyboard layout and a UK keyboard layout.
Try experimenting using the following two test cases:
- Press and hold the
shift
key, then presskey 2
and release it. Next, release theshift
key. - Press and hold the
shift
key, then press and holdkey 2
. Release theshift
key. Finally, releasekey 2
.
HTML
<div class="fx">
<div>
<textarea rows="5" name="test-target" id="test-target"></textarea>
<button type="button" name="btn-clear-console" id="btn-clear-console">clear console</button>
</div>
<div class="flex">
<div id="console-log"></div>
</div>
</div>
CSS
.fx {
-webkit-display: flex;
display: flex;
margin-left: -20px;
margin-right: -20px;
}
.fx > div {
padding-left: 20px;
padding-right: 20px;
}
.fx > div:first-child {
width: 30%;
}
.flex {
-webkit-flex: 1;
flex: 1;
}
#test-target {
display: block;
width: 100%;
margin-bottom: 10px;
}
JavaScript
let textarea = document.getElementById('test-target'),
consoleLog = document.getElementById('console-log'),
btnClearConsole = document.getElementById('btn-clear-console');
function logMessage(message) {
let p = document.createElement('p');
p.appendChild(document.createTextNode(message));
consoleLog.appendChild(p);
}
textarea.addEventListener('keydown', (e) => {
if (!e.repeat)
logMessage(`first keydown event. key property value is "${e.key}"`);
else
logMessage(`keydown event repeats. key property value is "${e.key}"`);
});
textarea.addEventListener('beforeinput', (e) => {
logMessage(`beforeinput event. you are about inputing "${e.data}"`);
});
textarea.addEventListener('input', (e) => {
logMessage(`input event. you have just inputed "${e.data}"`);
});
textarea.addEventListener('keyup', (e) => {
logMessage(`keyup event. key property value is "${e.key}"`);
});
btnClearConsole.addEventListener('click', (e) => {
let child = consoleLog.firstChild;
while (child) {
consoleLog.removeChild(child);
child = consoleLog.firstChild;
}
});
Result
Case 1
When the shift key is pressed, a keydown
event is first fired, and the key
property value is set to the string "Shift"
. As we keep holding this key, the keydown
event does not continue to fire repeatedly because it does not produce a character key.
When key 2
is pressed, another keydown
event is fired for this new key press, and the key
property value for the event is set to the string "@"
for the U.S keyboard type and """
for the UK keyboard type, because of the active modifier shift
key. The beforeinput
and input
events are fired next because a character key has been produced.
As we release the key 2
, a keyup
event is fired and the key
property will maintain the string values "@"
and """
for the different keyboard layouts respectively.
As we finally release the shift
key, another keyup
event is fired for it, and the key attribute value remains "Shift"
.
Case 2
When the shift key is pressed, a keydown
event is first fired, and the key
property value is set to be the string "Shift"
. As we keep holding this key, the keydown event does not continue to fire repeatedly because it produced no character key.
When key 2
is pressed, another keydown
event is fired for this new key press, and the key
property value for the event is set to be the string "@"
for the U.S keyboard type and """
for the UK keyboard type, because of the active modifier shift
key. The beforeinput
and input
events are fired next because a character key has been produced. As we keep holding the key, the keydown
event continues to fire repeatedly and the KeyboardEvent.repeat
property is set to true
. The beforeinput
and input
events are fired repeatedly as well.
As we release the shift
key, a keyup
event is fired for it, and the key attribute value remains "Shift"
. At this point, notice that the key
property value for the repeating keydown event of the key 2
key press is now "2" because the modifier shift
key is no longer active. The same goes for the InputEvent.data
property of the beforeinput
and input
events.
As we finally release the key 2
, a keyup
event is fired but the key
property will be set to the string value "2"
for both keyboard layouts because the modifier shift
key is no longer active.
Example
This example uses EventTarget.addEventListener()
to listen for keydown
events. When they occur, the key's value is checked to see if it's one of the keys the code is interested in, and if it is, it gets processed in some way (possibly by steering a spacecraft, perhaps by changing the selected cell in a spreadsheet).
window.addEventListener("keydown", function (event) {
if (event.defaultPrevented) {
return; // Do nothing if the event was already processed
}
switch (event.key) {
case "Down": // IE specific value
case "ArrowDown":
// Do something for "down arrow" key press.
break;
case "Up": // IE specific value
case "ArrowUp":
// Do something for "up arrow" key press.
break;
case "Left": // IE specific value
case "ArrowLeft":
// Do something for "left arrow" key press.
break;
case "Right": // IE specific value
case "ArrowRight":
// Do something for "right arrow" key press.
break;
case "Enter":
// Do something for "enter" or "return" key press.
break;
case "Escape":
// Do something for "esc" key press.
break;
default:
return; // Quit when this doesn't handle the key event.
}
// Cancel the default action to avoid it being handled twice
event.preventDefault();
}, true);
Specification
Specification | Status | Comment |
---|---|---|
Document Object Model (DOM) Level 3 Events Specification La definición de 'KeyboardEvent.key' en esta especificación. |
Obsolete | Initial definition, included key values. |
Browser compatibility
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