Javascript KeyboardEvent Tutorial

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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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