Manage maps of handlers for key events
KeyMap - Manage maps of handlers for key events
var rules = { // attach handlers to specific keys RETURN: function(event){doSomethingWith(event)}, C_DOWN: ctrlArrowDownHandler, C_S_F7: ctrlShiftF7Handler, // special rules using regular expressions REGEX: [ ["", /^[0-9]$/, digitHandler ], ["C_", /^[aeiou]$/i, ctrlVowelHandler] ], // use Ctrl-X as a prefix for another set of rules C_X: KeyMap.Prefix({R: ctrlX_R_handler, 4: ctrlX_4_handler}) }; // create a keymap object var aKeyMap = new KeyMap(rules);
// attach the corresponding handler to the keydown event (on document) aKeyMap.observe("keydown"); // other way to attach : manually insert handler document.onkeydown = aKeyMap.eventHandler({preventDefault: true, ignoreShift : true});
// dynamically change the map aKeyMap.rules.push(new_rules); // idem, temporarily ignore all keys aKeyMap.rules.push(KeyMap.MapAllKeys(function(){})); // back to previous handling state aKeyMap.rules.pop();
Provides an abstraction layer for associating handlers with HTML key events, in a browser-independent way.
A keymap is a stack of collections of rules. Each rule has a key specification or a regexp specification, and a handler to be called whenever the specification is met. The keymap object as a whole can then be registered as a usual HTML event handler associated to some DOM element (most often the document element), and will dispatch key events to appropriate handlers.
Key specifications look like A (key 'A'), C_S_A (control-shift-A), A_DELETE (alt-Delete). They are formed from :
For printable characters, the keyname is just that character; for special editing keys such as backspace, arrow up, etc., names are taken from the following list of builtins :
BACKSPACE ESCAPE TAB RETURN LINEFEED SPACE PAGE_UP PAGE_DOWN END HOME LEFT UP RIGHT DOWN INSERT DELETE PAUSE WINDOWS PRINT_SCREEN CAPS_LOCK NUM_LOCK SCROLL_LOCK F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11 F12 CTRL SHIFT ALT
Modifiers are specified through prefixes C_, S_ and A_, corresponding to key modifiers control, shift and alt. Several prefixes may be combined, but must appear in the order just given (so for example S_C_A would be illegal).
Alternatively, key specifications may also formed from key codes
instead of key names, so for example C_13
is equivalent to C_RETURN
.
For key codes 0-9, and additional '0' is required to avoid confusion
with digits: so C_09
is equivalent to C_TAB
, while C_9
means
"control-numeric 9".
In addition, keymap objects can also manage regex rules that cover several possible key events; details are given below.
Following the W3C event model, handlers called from the keymap object
receive an event object as argument. This is the usual HTML event
object, augmented with two properties keyName
and keyModifiers
,
computed according to the specifications given above. So for
example a simple handler can be
var myHandler = function (event) { alert(event.keyName + " was pressed with modifiers " + event.keyModifiers); }
Further propagation of the event to other handlers is cancelled by
default : W3C methods event.stopPropagation()
and
event.preventDefault()
are called automatically by the keymap
object (or, if running under Microsoft Internet Explorer, property
cancelBubble
is set to true and and property returnValue
is set
to false). This default behaviour can be disabled if necessary,
as explained below.
Keymaps may be attached to HTML elements on the
keydown
, keypress
or keyup
event types.
Choosing the proper event type is important, as it
affects not only the time at which events are fired,
but also the returned keycodes :
keydown
and keyup
These are "low-level" event types that capture almost every key on
the keyboard, including special keys like ESCAPE, F1, PAGE UP, etc.
Returned key codes remain at a raw level, i.e. they are not translated
into characters. This means that if Shift-1 is marked on your keyboard
as an exclamation mark, a plus sign, or some other special character,
you will not receive that keycode when capturing keydown
events :
rather, you will receive keycode 49 (ASCII character '1'). Similarly,
all letters are received as uppercase.
keypress
By contrast, the keypress
event type is higher-level in that it
performs the translation from keys to characters, according to your
specific keyboard. However, this event type only fires for
printable characters, so you cannot observe keypress
if
you intend to capture special keys such as arrow keys, function keys, etc.
In theory, attributes such as onkeydown
or onkeypress
may be
used with most HTML elements; but in practice, most of them will actually
never fire the key events! So the most common and most sensible way
for capturing key events is to attach to the document
element.
Events keypress
and keydown
will repeat if the
key is held down.
In order to attach the keymap to an element, you can either use the supplied /"observe" method, or call the /"eventHandler" method to get the keymap event handler, and then use your favorite technique to attach that handler to an element.
KeyMap
var myKeyMap = new KeyMap(rules);
Constructor for a keymap object.
The rules argument is a map from key specifications to handlers, like for example
{ A: function() {alert("pressed 'A'");}, S_TAB: function() {alert("pressed 'Shift-Tab'");}, CTRL: function() {alert("pressed the 'Ctrl' key");}, 10: function() {alert("pressed 'Linefeed' or maybe 'Ctrl-Return'");} }
Each key specification in the map corresponds to exacly one key
combination, so for example S_TAB
will not fire if the user pressed
Ctrl-Shift-Tab
.
For situations where several key combination will
fire the same handler, you can insert a REGEX
entry in the map.
This should be an array of triplets, where each triplet is of shape
[modifiers, regex, handler]
, like for example
var regexRules = [["C_", "[0-9]", myCtrlDigitHandler], ["C_S_", /^[AEIOU]$/, myCtrlShiftVowelHandler], [null, "RETURN|TAB|ESCAPE", someOtherHandler] ];
Whenever a key event is received, it is converted into a keyname, and then that keynames is compared against the regex rules, in order : the first rule that matches calls the corresponding handler and terminates the event handling process.
More specifically, the members of rule triplets are :
A string specifiying the key modifiers for which the rule will fire;
the string a concatenation of C_, S_ and A_, as explained above.
An empty string means that the rule only fires when no modifiers
are pressed. By contrast, a null
value specifies that
modifiers are ignored (the rule fires in any case).
Either a string containing a regular expression, or an already built
Javascript RegExp object. Strings will be automatically converted
to regular expressions, with start anchor ^
and end anchor $
automatically added. If you supply an already built RegExp object,
make sure to deal properly with the anchors; otherwise the rule
might fire in unexpected cases (for example the plain regex /[AEIOU]/
would match any builtin keyname like RETURN
or ESCAPE
, which
is probably not the intended meaning of the rule).
The function to be called when the rule succeeds.
An ANTIREGEX
entry in the map
works exactly like a REGEX
, except that
the handler is called when the regex does
not match. This is useful if you want to
catch most key events, except
a given set.
eventHandler
document.onkeydown = aKeyMap.eventHandler(options);
Generates an event handler that can be attached to an HTML element.
This method is called internally by the /"observe" method.
Use eventHandler
directly if you need fine control
on how the handler is attached to the dynamic HTML model.
The options
argument is optional. If present, it should be an
inline object containing truth values for the following
keys :
ignoreCtrl
ignore the Ctrl
keyboard modifier
ignoreShift
ignore the Shift
keyboard modifier
ignoreAlt
ignore the Alt
keyboard modifier
stopPropagation
stop propagation of the event
preventDefault
prevent default navigator behaviour on that event
For example if ignoreCtrl
is true, then the key
specification "C_S_TAB"
would
never fire, because Ctrl-Shift-TAB key events would be encoded merely
as "S_TAB"
.
observe
aKeyMap.observe(eventType, htmlElement, options);
This is the preferred way for attaching the keymap object to an HTML
element, on a given event type (keydown
, keypress
or keyup
).
Arguments are optional. The default event type is "keydown"
,
and the default element is document
.
Options are passed to the /"eventHandler" method.
If not explicitly given, the options default
to undefined
except for event type keypress
, where
ignoreShift
defaults to true
. The reason is that the Shift
modifier heavily depends on which keyboard the user is using, and
often the user really has no choice on pressing or not the Shift key
(this would generate a different keycode). So it makes sense to just
stop paying attention to the Shift key for keypress
events.
rules
aKeyMap.rules.push(new_rules); aKeyMap.rules.pop();
A DHTML application may need to temporarily change the key handlers (for
example when switching from navigation mode to editing mode).
Therefore, a keymap object actually holds a stack of rules
and publishes this stack in its rules
property.
Rules pushed on top of that stack will take precedence over
pre-existing rules; conversely, popping from the stack
restores the keymap to its previous state.
MapAllKeys
// grab all keys aKeyMap.rules.push(KeyMap.MapAllKeys(my_handler)); // ignore all keys aKeyMap.rules.push(KeyMap.MapAllKeys(function (){}));
Convenience function to build a regex rule that matches all keys.
Prefix
main_rules = {C_X: KeyMap.Prefix({R: ctrlX_R_handler, 4: ctrlX_4_handler})};
Specifies that a key (here Ctrl-X
) is a prefix to another
set of rules : the next key event will be passed to these rules,
and after that the main rules resumes normal behaviour.
Hence you can attach handlers to sequences of keys, like for
example in Emacs.