Javascript KeyboardEvent Tutorial

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KeyboardEvent
Properties & Methods
Table: Key, KeyCode

1- KeyboardEvent

KeyboardEvent is an interface that represents events occurring when users interact with a keyboard, including keydown, keypress, keyup events.

KeyboardEvent is subinterface of UIEvent.

TODO Link?

Order	Event
1	onkeydown
2	onkeypress
3	onkeyup

keydown

The keydown event occurs when you press down a key. In Windows OS, If you continue to keep the key pressed, it will constantly emit keydown & keypress events. But in MacOS, If you continue to keep the key pressed, it will constantly emit keydown events. Like the following illustration.

keypress

There are 2 cases of occurence of the keypress, in which case 1 is explained above by me (View the keydown event). Case 2 is that you press down a key and quickly release it, and at this time there will be 2 events such as keypress, keyup emitted in the order.

keyup

The keyup event occurs when you release a key.

Note: The keypress event will not be emitted for the keys such as ALT, SHIFT, CTRL, META-KEY, ESC. If you want to detect whether those keys are being pressed, you can use the properties such as altKey, shiftKey, ctrlKey, metaKey of the event object.

keyevents-example.html

<!DOCTYPE html>
<html>
   <head>
      <title>KeyEvent Example</title>

      <script src="keyevents-example.js"></script>

   </head>
   <body>

      <h3>KeyEvent example</h3>

      <input type="text"
            onkeydown="keydownHandler(event)"
            onkeyup="keyupHandler(event)"
            onkeypress="keypressHandler(event)"/>
      <br/><br/>

      <textarea id="log-div" rows = "10" disabled>

      </textarea>
      <br/>
      <button onclick="clearLog()">Clear</button>

   </body>
</html>

keyevents-example.js


function keydownHandler(evt)  {
    appendLog("Keydown!");
}

function keyupHandler(evt)  {
    appendLog("Keyup!");
}

function keypressHandler(evt)  {
    appendLog("Keypress!");
}


function appendLog(text)  {
    var oldText = document.getElementById("log-div").value;
    document.getElementById("log-div").value = oldText+"\n"+ text;
}

function clearLog()  {
    document.getElementById("log-div").value = "";
}

2- Properties & Methods

KeyEvent is the sub-interface of UIEvent, therefore, it inherits the properties and methods from this interface.

TODO Link?

Property	Description
altKey	Returns true if the "ALT" key is being pressed when a key event occurs.
ctrlKey	Returns true if the "CTRL" key is being pressed when a key event occurs.
shiftKey	Returns true if the "SHIFT" key is being pressed when a key event occurs.
metaKey	Returns true if the "META" đkey is being pressed when a key event occurs.

Eample: Press the 'SHIFT' key and keep it unchanged and then press any key.

prop-shiftKey-example.html

<!DOCTYPE html>
<html>
   <head>
      <title>KeyEvent Example</title>

      <script src="prop-shiftKey-example.js"></script>

   </head>
   <body>

      <h3>Hold key 'SHIFT' and press any key!</h3>

      <input type="text"
            onkeydown="keydownHandler(event)"/>
      <br/><br/>

      <div id="log-div" style="color:red;"></div>

   </body>
</html>

prop-shiftKey-example.js


function keydownHandler(evt)  {

   if(evt.shiftKey) {
      document.getElementById("log-div").innerHTML ="evt.shiftKey = true";
   } else {
      document.getElementById("log-div").innerHTML ="evt.shiftKey = false";
   }

}

Property	Description
keyCode	Returns the Unicode character code of the key that triggered the keypress event, or the Unicode key code of the key that triggered the keydown or keyup event
key	Returns the key name. For example: (enter, shift, 0, 1, a, b,....)

charCode	Returns the Unicode character code of the key that triggered the keypress event. Note: charCode = 0 on keydown, keyup event.
code	Returns the key name. For example: (Enter, Shift, Digit0, Digit1, KeyA, KeyB,...)

which	Returns charCode on keypress event, or keyCode on keydown, keyup event

keyCode, key:

Each key on the keyboard has one number representing for it, referred to as keyCode. For example, the 'a' key has keyCode = 65. There is no concept of uppercase and lowercase for keys. So the keyCode of 'a' or 'A' is 65.

keyCode	key (name of key)
...
9	tab
12	clear
13	enter
...
48	0
49	1
50	2
51	3
....
65	a
66	b
67	c
.....

** You can view the details of the Key & KeyCode table in the appendix at the end of this post.

prop-key-keyCode-example.html

<!DOCTYPE html>
<html>
   <head>
      <title>KeyEvent Example</title>

      <script>
          function keydownHandler(evt) {
            var logDiv = document.getElementById("log-div");

            logDiv.innerHTML = "event.key= " + evt.key +"<br/>"
                             + "event.keyCode= "+ evt.keyCode;
          }
      </script>

   </head>
   <body>

      <h3>event.key, event.keyCode</h3>

      <input type="text" onkeydown="keydownHandler(event)"/>
      <br/><br/>

      <div id="log-div" style="color:red;"></div>
   </body>
</html>

code, charCode

keyCode	key (Name of key)	code (Name of key)
.....
16	shift	ShiftLeft
.....
48	0	Digit0
49	1	Digit1
50	2	Digit2
51	3	Digit3
....
65	a	KeyA
66	b	KeyB
67	c	KeyC
68	d	KeyD
69	e	KeyE
.....

charCode is assigned a value only in the keypress event, it always has the value of 0 in the keydown & keyup event. charCode is a number that represents an Unicode character pressed by an user.

prop-code-charCode-example.html

<!DOCTYPE html>
<html>
   <head>
      <title>KeyEvent Example</title>

      <script>
          function keypressHandler(evt) {
            var logDiv = document.getElementById("log-div");

            logDiv.innerHTML = "event.code= " + evt.code +"<br/>"
                             + "event.charCode= "+ evt.charCode;
          }
      </script>

   </head>
   <body>

      <h3>event.code, event.charCode</h3>

      <input type="text" onkeypress="keypressHandler(event)"/>
      <br/><br/>

      <div id="log-div" style="color:red;"></div>

   </body>
</html>

keyCode vs charCode

key	keyCode (keydown/keyup)	keyCode (keypress)	charCode (keypress)
.....
a/A	65 / 65	97 / 65	97 / 65
b/B	66 / 66	98 / 66	98 / 66
c/C	67 / 67	99 / 67	99 / 67
d/D	68 / 68	100 / 68	100 / 68
e/E	69 / 69	101 / 69	101 / 69
.....

Property	Description
isComposing	Returns true if the state of the event is composing. Otherwise, returns false.
location	Returns the location of a key on the keyboard or device
repeat	Returns true if a key is being hold down repeatedly. Otherwise, returns false.

Method	Description
getModifierState()	Returns true if the specified key is activated

3- Table: Key, KeyCode

keyCode	Key (Name of key).
0	That key has no keycode
3	break
8	backspace / delete
9	tab
12	clear
13	enter
16	shift
17	ctrl
18	alt
19	pause/break
20	caps lock
21	hangul
25	hanja
27	escape
28	conversion
29	non-conversion
32	spacebar
33	page up
34	page down
35	end
36	home
37	left arrow
38	up arrow
39	right arrow
40	down arrow
41	select
42	print
43	execute
44	Print Screen
45	insert
46	delete
47	help
48	0
49	1
50	2
51	3
52	4
53	5
54	6
55	7
56	8
57	9
58	:
59	semicolon (firefox), equals
60	<
61	equals (firefox)
63	ß
64	@ (firefox)
65	a
66	b
67	c
68	d
69	e
70	f
71	g
72	h
73	i
74	j
75	k
76	l
77	m
78	n
79	o
80	p
81	q
82	r
83	s
84	t
85	u
86	v
87	w
88	x
89	y
90	z
91	Windows Key / Left ⌘ / Chromebook Search key
92	right window key
93	Windows Menu / Right ⌘
95	sleep
96	numpad 0
97	numpad 1
98	numpad 2
99	numpad 3
100	numpad 4
101	numpad 5
102	numpad 6
103	numpad 7
104	numpad 8
105	numpad 9
106	multiply
107	add
108	numpad period (firefox)
109	subtract
110	decimal point
111	divide
112	f1
113	f2
114	f3
115	f4
116	f5
117	f6
118	f7
119	f8
120	f9
121	f10
122	f11
123	f12
124	f13
125	f14
126	f15
127	f16
128	f17
129	f18
130	f19
131	f20
132	f21
133	f22
134	f23
135	f24
144	num lock
145	scroll lock
160	^
161	!
162	؛ (arabic semicolon)
163	#
164	$
165	ù
166	page backward
167	page forward
168	refresh
169	closing paren (AZERTY)
170	*
171	~ + * key
172	home key
173	minus (firefox), mute/unmute
174	decrease volume level
175	increase volume level
176	next
177	previous
178	stop
179	play/pause
180	e-mail
181	mute/unmute (firefox)
182	decrease volume level (firefox)
183	increase volume level (firefox)
186	semi-colon / ñ
187	equal sign
188	comma
189	dash
190	period
191	forward slash / ç
192	grave accent / ñ / æ / ö
193	?, / or °
194	numpad period (chrome)
219	open bracket
220	back slash
221	close bracket / å
222	single quote / ø / ä
223	`
224	left or right ⌘ key (firefox)
225	altgr
226	< /git >, left back slash
230	GNOME Compose Key
231	ç
233	XF86Forward
234	XF86Back
235	non-conversion
240	alphanumeric
242	hiragana/katakana
243	half-width/full-width
244	kanji
251	unlock trackpad (Chrome/Edge)
255	toggle touchpad

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