Detecting support for event types

[RobG]

When using createEvent, an eventType parameter must be provided as an
argument. This can be one of those specified in DOM 2 or 3 Events, or
it might be a proprietary eventType[1].

My problem is testing for support of particular eventTypes - the DOM 2
Events Interface DocumentEvent says that if the eventType is not
supported, it throws a DOM exception[2]. This makes testing rather
tough - if you try something like:

if (document && document.create Event &&
document.create Event(eventType )) {...}

or a typeof test and the eventType (say 'MouseEvents') isn't
supported, the script crashes with a DOM execption as specified in the
DOM 2 Events spec. I can do try..catch but I'd rather not if I can
avoid it:

var eventType = 'MouseEvents';
try {
document.create Event(eventType );
alert(eventType + ' OK');
} catch (e) {
alert(eventType + ' not supported by createEvent');
return;
}


Is there a feature test that can be used?


1. Gecko supporte eventTypes:
<URL: http://developer.mozilla.org/en/docs...nt.createEvent

>

2. W3C DOM 2 Events: Interface DocumentEvent - createEvent
<URL: http://www.w3.org/TR/DOM-Level-2-Eve...nt-createEvent

>

--
Rob

[RobG]

Re: Detecting support for event types

On Aug 15, 2:04 pm, RobG <rg...@iinet.ne t.auwrote:

When using createEvent, an eventType parameter must be provided as an
argument.

While I'm at it, is there a list somewhere of the events that belong
to each event type (e.g. click, mouseup and mousedown belong to
MouseEvents while focus and blur belong to UIEvents), or do I have to
guess them and test by trial and error?


--
Rob

[Martin Honnen]

Re: Detecting support for event types

RobG wrote:

While I'm at it, is there a list somewhere of the events that belong
to each event type (e.g. click, mouseup and mousedown belong to
MouseEvents while focus and blur belong to UIEvents), or do I have to
guess them and test by trial and error?

The W3C DOM Level 2 Events specification lists events, for instance see

http://www.w3.org/TR/DOM-Level-2-Events/events.html#Events-UIEvent

then you will find DOMFocusIn, DOMFocusOut, and DOMActivate.

--

Martin Honnen

http://JavaScript.FAQTs.com/

[Peter Michaux]

Re: Detecting support for event types

On Aug 14, 9:04 pm, RobG <rg...@iinet.ne t.auwrote:

When using createEvent, an eventType parameter must be provided as an
argument.  This can be one of those specified in DOM 2 or 3 Events, or
it might be a proprietary eventType[1].
>
My problem is testing for support of particular eventTypes - the DOM 2
Events Interface DocumentEvent says that if the eventType is not
supported, it throws a DOM exception[2].  This makes testing rather
tough - if you try something like:
>
  if (document && document.create Event &&
document.create Event(eventType )) {...}
>
or a typeof test and the eventType (say 'MouseEvents') isn't
supported, the script crashes with a DOM execption as specified in the
DOM 2 Events spec.  I can do try..catch but I'd rather not if I can
avoid it:
>
  var eventType = 'MouseEvents';
  try {
    document.create Event(eventType );
    alert(eventType + ' OK');
  } catch (e) {
    alert(eventType + ' not supported by createEvent');
    return;
  }
>
Is there a feature test that can be used?

Second paragraph here

<URL: http://www.w3.org/TR/DOM-Level-2-Events/events.html#Eve nts-eventgroupings-mouseevents>

indicates something like the following would be sufficient

if (typeof document == 'object' && document &&
document.implem entation &&
document.implem entation.hasFea ture &&
document.implem entation.hasFea ture('MouseEven ts', 2.0))

But the browser may well still be lying as this implies the
MouseEvents interface is present *and* works. Evidence has shown that
many features are present in browsers but don't work. This may be too
paranoid.

See also Flanagan's 5th edition page 314 for a list of module names
that can be used for hasFeature, page 404 in the events section, and
page 776 in the reference section. (Flanagan's 4th edition has the
same content indexed.)

Peter

[RobG]

Re: Detecting support for event types

On Aug 18, 10:14 am, Peter Michaux <petermich...@g mail.comwrote:

On Aug 14, 9:04 pm, RobG <rg...@iinet.ne t.auwrote:
>
>
>

When using createEvent, an eventType parameter must be provided as an
argument. This can be one of those specified in DOM 2 or 3 Events, or
it might be a proprietary eventType[1].

>

My problem is testing for support of particular eventTypes - the DOM 2
Events Interface DocumentEvent says that if the eventType is not
supported, it throws a DOM exception[2]. This makes testing rather
tough - if you try something like:

>

if (document && document.create Event &&
document.create Event(eventType )) {...}

>

or a typeof test and the eventType (say 'MouseEvents') isn't
supported, the script crashes with a DOM execption as specified in the
DOM 2 Events spec. I can do try..catch but I'd rather not if I can
avoid it:

>

var eventType = 'MouseEvents';
try {
document.create Event(eventType );
alert(eventType + ' OK');
} catch (e) {
alert(eventType + ' not supported by createEvent');
return;
}

>

Is there a feature test that can be used?

>
Second paragraph here
>
<URL:http://www.w3.org/TR/DOM-Level-2-Events/events.html#Eve nts-eventgroup...>
>
indicates something like the following would be sufficient
>
if (typeof document == 'object' && document &&
document.implem entation &&
document.implem entation.hasFea ture &&
document.implem entation.hasFea ture('MouseEven ts', 2.0))

Looks familiar... :-)

But the browser may well still be lying as this implies the
MouseEvents interface is present *and* works. Evidence has shown that
many features are present in browsers but don't work. This may be too
paranoid.

I don't think it's paranoid, just common sense. The W3C hasFeature is
no better than feature inference, it doesn't actually test for
support. It would have been much better (though still not sufficient)
if they'd specified hasFeature return null for unsupported eventTypes,
like getElementById does if there's no element with the specified id.

See also Flanagan's 5th edition page 314 for a list of module names
that can be used for hasFeature, page 404 in the events section, and
page 776 in the reference section. (Flanagan's 4th edition has the
same content indexed.)

Yeah, looked there. Following Martin's advice I created my own list
from various sources, here's what I have so far:

var allFeatures = {

Safari : ['TouchEvent', 'GestureEvent'],

Gecko : ['MessageEvent', 'MouseScrollEve nts', 'PopupEvents',
'PopupBlockedEv ents', 'XULCommandEven t',
'XULCommandEven ts'],

SVG : ['SVGEvents', 'SVGEvent', 'SVGZoomEvents' ,
'SVGZoomEvent'],

DOM2 : ['UIEvents', 'MouseEvents', 'MutationEvents ',
'HTMLEvents'],

DOM3 : ['UIEvent', 'MouseEvent', 'MutationEvent' ,
'MutationNameEv ent', 'TextEvent', 'TextEvents',
'KeyboardEvent' , 'KeyEvents', 'Event', 'Events']
};


and the supported events for each interface (wrapped for posting, not
all features added yet):

var ifaces = {
UIEvents : 'DOMFocusIn DOMFocusOut DOMActivate',

MouseEvents : 'click mousedown mouseup mouseover mousemove'
+ ' mouseout',

MutationEvent : 'DOMSubtreeModi fied DOMNodeInserted '
+ ' DOMNodeRemoved DOMNodeRemovedF romDocument'
+ ' DOMNodeInserted IntoDocument DOMAttrModified '
+ ' DOMCharacterDat aModified',

HTMLEvents : 'load unload abort error select change'
+ ' submit reset focus blur resize scroll',

// Draft events
TouchEvent : 'touchstart touchmove touchend touchcancel',

GestureEvent : 'gesturestart gesturechange gestureend'
};


I'm still working on the best way to organise them, I need to study
the W3C specs more. Perhaps I need to use hasFeature first, then
try..catch. The idea is to have a pre-calculated list of supported
event interfaces and types, then allow calling them by:

sendEvent( elementId, eventType [, parameterObject])

where each event type has a default parameter object that can be
modified by passing an object with just the parameters that need to be
set to some other value.

The event interface to use with createEvent is calculated from the
list of supported interfaces. If the appropriate interface isn't
supported, the event isn't dispatched.

All this started because I wanted to know a good way of detecting
support for touch events and expanded to be a more general way to send
any event into the DOM.

It seems Mozilla has changed its position on dispatchEvent. I'm
pretty sure that in Firefox 2 when a click event was fired on a link
using dispatchEvent, it follow the link, but Firefox 3 doesn't (nor
does IE using fireEvent), Safari 3 does. I haven't got to testing
other browsers but I expect this will only work in fairly modern
versions.

Maybe I'll go back to my original plan and do this just for touch
events.


--
Rob

[Peter Michaux]

Re: Detecting support for event types

On Aug 17, 6:13 pm, RobG <rg...@iinet.ne t.auwrote:

[snip]

I'm still working on the best way to organise them, I need to study
the W3C specs more. Perhaps I need to use hasFeature first, then
try..catch.

What does that gain over just using try-catch? The only issue with try-
catch is it may syntax error in old browsers.

The idea is to have a pre-calculated list of supported
event interfaces and types, then allow calling them by:
>
sendEvent( elementId, eventType [, parameterObject])
>
where each event type has a default parameter object that can be
modified by passing an object with just the parameters that need to be
set to some other value.

This reads like prototype-based inheritance and I find it is rare to
actually find situations where prototype-based inheritance is so
appropriate.

The event interface to use with createEvent is calculated from the
list of supported interfaces. If the appropriate interface isn't
supported, the event isn't dispatched.

The way my feature testing has evolved would mean this "failure" is
too late. If the DOM has been manipulated and then depends on this
dispatch being successful and the dispatch will fail then the DOM
never should have been manipulated in the first place. In other words,
a widget isn't initialized unless it can be fully functional.

All this started because I wanted to know a good way of detecting
support for touch events

Apple's documentation is disappointingly dependent on
navigator.userA gent parsing.

and expanded to be a more general way to send
any event into the DOM.

I've never had any need for production code to send and even to a DOM
element. Do you?

Sending events to DOM elements could be useful in a test library.
Selenium does this but the code specific to each browser is a little
scary (admittedly they are writing something difficult.)

It seems Mozilla has changed its position on dispatchEvent. I'm
pretty sure that in Firefox 2 when a click event was fired on a link
using dispatchEvent, it follow the link, but Firefox 3 doesn't (nor
does IE using fireEvent), Safari 3 does. I haven't got to testing
other browsers but I expect this will only work in fairly modern
versions.
>
Maybe I'll go back to my original plan and do this just for touch
events.

What does something like
document.implem entation.hasFea ture('TouchEven t', 1.0) return?

Peter

[Thomas 'PointedEars' Lahn]

Re: Detecting support for event types

RobG wrote:

When using createEvent, an eventType parameter must be provided as an
argument. This can be one of those specified in DOM 2 or 3 Events, or
it might be a proprietary eventType[1].
>
My problem is testing for support of particular eventTypes - the DOM 2
Events Interface DocumentEvent says that if the eventType is not
supported, it throws a DOM exception[2]. This makes testing rather
tough - if you try something like:
>
if (document && document.create Event &&
document.create Event(eventType )) {...}
>
or a typeof test and the eventType (say 'MouseEvents') isn't
supported, the script crashes with a DOM execption as specified in the
DOM 2 Events spec.

It does _not_ really *crash* with the exception; the method *throws* the
(runtime) exception and you missed catching it.

I can do try..catch but I'd rather not if I can avoid it:

You cannot avoid it, this is exactly what the exception and consequently the
TryStatement with a Catch part is for. It has been learned from e.g. Java
that exceptions allow subroutines to return to their caller with a failure
state immediately, and exception handling allows the caller to recognize and
handle that state, without having to define a return value for each kind of
failure which would then no longer be available as return value for proper
execution.

var eventType = 'MouseEvents';
try {

You should add the "supposedly callable" feature test here, see below.

document.create Event(eventType );
>
alert(eventType + ' OK');
} catch (e) {
alert(eventType + ' not supported by createEvent');
return;
}
>
Is there a feature test that can be used?

try...catch can be eval()'d to hide it from incompatible parsers:

/**
* Wrapper for safer <code>try</code>...<code>c atch</code>.
*
* Attempts to evaluate a value as a <i>StatementLis t</i>, and attempts
* to evaluate another value as a <i>StatementLis t</iif an exception
* is thrown in the process. The argument identifiers may be used
* in each value to refer to the used values; the <code>code</code>
* word may be used to the refer to the entire constructed
* <code>try</code>...<code>c atch</codestring that is evaluated
* as a <i>Program</i>.
*
* @param statements
* Value to be evaluated as a <i>StatementLis t</i>.
* Called if a <code>Functio n</codeobject reference, converted
* to string if not a string, and used as-is otherwise.
* For compatibility, the <code>undefined </codevalue
* is evaluated like the empty string.
* @param errorHandlers
* Value to be evaluated as a <i>StatementLis t</iin case of an
* exception. Called if a <code>Functio n</codeobject reference,
* converted to string if not a string, and used as-is otherwise.
* For compatibility, the <code>undefined </codevalue
* is evaluated like the empty string.
* @return
* The result of <code>statement s</code>, or the result
* of <code>errorHand lers</codeif an error occurred.
* @author
* Copyright (c) 2008
* Thomas 'PointedEars' Lahn &lt;js@PointedE ars.de&gt;
* Distributed under the GNU GPL v3 and later.
* @partof JSX:exception.j s
*/
function tryThis(stateme nts, errorHandlers)
{
/**
* @param s Value to be stringified
* @return Stringified version of <code>s</code>
*/
function stringify(s)
{
if (typeof s == "function")
{
s = "(" + s + ")()";
}
else if (typeof s == "undefined" )
{
s = "";
}

return s;
}

statements = stringify(state ments);
errorHandlers = stringify(error Handlers);

var code = 'try { ' + statements + ' }'
+ 'catch (e) { ' + errorHandlers + ' }';

return eval(code);
}

var eventType = 'MouseEvents';
tryThis(
function() {
if (isMethod(docum ent, "createEven t"))
{
document.create Event(eventType );
window.alert(ev entType + ' OK');
}
},
function() {
window.alert(ev entType + ' not supported by createEvent');
});


HTH

PointedEars
--
Prototype.js was written by people who don't know javascript for people
who don't know javascript. People who don't know javascript are not
the best source of advice on designing systems that use javascript.
-- Richard Cornford, cljs, <f806at$ail$1$8 300dec7@news.de mon.co.uk>

[RobG]

Re: Detecting support for event types

On Aug 18, 12:09 pm, Peter Michaux <petermich...@g mail.comwrote:

On Aug 17, 6:13 pm, RobG <rg...@iinet.ne t.auwrote:
>
[snip]
>

I'm still working on the best way to organise them, I need to study
the W3C specs more. Perhaps I need to use hasFeature first, then
try..catch.

>
What does that gain over just using try-catch?

If it returns false, don't even bother with the W3C event model.

I'm still not clear about the difference between the event model and
the Events *module* - does hasFeature('Eve nts', '2.0') just mean
support for interface Event, or does it mean all of the interfaces for
the event model (Event, DocumentEvent, EventListener, EventTarget) but
not the extra ones like UIEvents, MutationEvents, etc.?

Anyhow, I figured hasFeaure might circumvent using try..catch on
interfaces where the module itself isn't supported, e.g. there are 7
interfaces in MutationEvent, if hasFeature(‘Mut ationEvents’,’2 .0’)
returns false, that's 7 try..catch calls that can be avoided. I
figure it's more likely browsers will pretend to support modules than
not, or only implement part of them. Testing will reveal.

The only issue with try-
catch is it may syntax error in old browsers.

Yes, Thomas has posted a solution that I'll file away if it's really
needed.

The idea is to have a pre-calculated list of supported
event interfaces and types, then allow calling them by:

>

sendEvent( elementId, eventType [, parameterObject])

>

where each event type has a default parameter object that can be
modified by passing an object with just the parameters that need to be
set to some other value.

>
This reads like prototype-based inheritance and I find it is rare to
actually find situations where prototype-based inheritance is so
appropriate.

No, I have an isSupported method so you'd call:

if (isSupported('U IEvents')) {


The pre-calculated list is kept in isSupported using a closure and is
used so that the feature test doesn't have to happen every time.

The event interface to use with createEvent is calculated from the
list of supported interfaces. If the appropriate interface isn't
supported, the event isn't dispatched.

>
The way my feature testing has evolved would mean this "failure" is
too late. If the DOM has been manipulated and then depends on this
dispatch being successful and the dispatch will fail then the DOM
never should have been manipulated in the first place. In other words,
a widget isn't initialized unless it can be fully functional.

It can use the same isSupported test.

All this started because I wanted to know a good way of detecting
support for touch events

>
Apple's documentation is disappointingly dependent on
navigator.userA gent parsing.
>

and expanded to be a more general way to send
any event into the DOM.

>
I've never had any need for production code to send and even to a DOM
element. Do you?

No, but although that isn't where I started it seems to be where I'm
headed. The goal is a feature test for touch events. One approach is
to attach an ontouchstart (or some other touch event) listener and
fire it using dispatchEvent it to see what happens - it seems very
crude but was a starting point. Along the way it occurred to me that
detecting support for the TouchEvent interface might be sufficient and
a little more elegant. Then I got a bit sidetracked into a more
general detection of event modules...

Sending events to DOM elements could be useful in a test library.
Selenium does this but the code specific to each browser is a little
scary (admittedly they are writing something difficult.)

I think I prefer the 'unobtrusive' approach - if it doesn't look like
it'll work, don't attempt it and fallback to simpler stuff.

It seems Mozilla has changed its position on dispatchEvent. I'm
pretty sure that in Firefox 2 when a click event was fired on a link
using dispatchEvent, it follow the link, but Firefox 3 doesn't (nor
does IE using fireEvent), Safari 3 does. I haven't got to testing
other browsers but I expect this will only work in fairly modern
versions.

>

Maybe I'll go back to my original plan and do this just for touch
events.

>
What does something like
document.implem entation.hasFea ture('TouchEven t', 1.0) return?

I don't know, Apple's documentation doesn't provide any hints on the
version number or whether it should work with hasFeature - '1.0' is as
good a guess as any, I'll try it later. :-)


--
Rob

[RobG]

Re: Detecting support for event types

On Aug 18, 4:45 pm, RobG <rg...@iinet.ne t.auwrote:

On Aug 18, 12:09 pm, Peter Michaux <petermich...@g mail.comwrote:

[...]

What does something like
document.implem entation.hasFea ture('TouchEven t', 1.0) return?

>
I don't know, Apple's documentation doesn't provide any hints on the
version number or whether it should work with hasFeature - '1.0' is as
good a guess as any, I'll try it later.  :-)

I tried all version numbers from '0.0' to '3.9', all returned false.


--
Rob

[RobG]

Re: Detecting support for event types

On Aug 18, 9:26 pm, RobG <rg...@iinet.ne t.auwrote:

On Aug 18, 4:45 pm, RobG <rg...@iinet.ne t.auwrote:
>

On Aug 18, 12:09 pm, Peter Michaux <petermich...@g mail.comwrote:

[...]

What does something like
document.implem entation.hasFea ture('TouchEven t', 1.0) return?

>

I don't know, Apple's documentation doesn't provide any hints on the
version number or whether it should work with hasFeature - '1.0' is as
good a guess as any, I'll try it later.  :-)

>
I tried all version numbers from '0.0' to '3.9', all returned false.

Here's my final effort:

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<title>TouchEve nt feature test</title>
<script type="text/javascript">

/* Feature tests for TouchEvent and GestureEvent modules
* implemented in Mobile Safari on iPhone
*
* The TouchEvent module is a draft (18/08/2008) that supports:
*
* touchstart
* touchmove
* touchend
* touchcancel
*
* The GestureEvent module is a draft (18/08/2008)
* that supports:
*
* gesturestart
* gesturechange
* gestureend
*
* The functions require support for try..catch, introduced
* in ECMA-262 ed3, JavaScript 1.4 and JScript 5.1.5010.
* Equates to Navigator 4.0 or later and IE 5.1 or later
* (http://pointedears.de/scripts/es-matrix/)
*
* If W3C DOM 2 Event document.create Event is supported,
* return either true or false,
* otherwise return undefined.
*/
function touchSupported( ) {
if (document && document.create Event) {
try {
document.create Event('TouchEve nt');
return true;
} catch (e) {
return false;
}
}
}

function gestureSupporte d() {
if (document && document.create Event) {
try {
document.create Event('GestureE vent');
return true;
} catch (e) {
return false;
}
}
}

/* Alternative hasTouch variable
*
* Example:
*
* if (hasTouches) {
* // assign touch and gesture events
* }
*/
var hasTouch = (function(){
if (document && document.create Event) {
try {
document.create Event('GestureE vent');
document.create Event('TouchEve nt');
return true;
} catch (e) {
return false;
}
}
})();
</script>
</head>
<body>
<div>
<button onclick="
alert('TouchEve nt supported: ' + touchSupported( ));
">Touch supported</button>
<button onclick="
alert('GestureE vent supported: ' + gestureSupporte d());
">Gesture supported</button>
<button onclick="
alert('Touch and gestures supported: ' + hasTouch);
">Touch and gestures supported</button>
</div>
</body>
</html>


--
Rob

[Beez]

Re: Detecting support for event types

Here's my final effort:

I tested this using IE 7.0.5730.11CO and I get ": undefined" for all
three tests. Is this expected?

[RobG]

Re: Detecting support for event types

On Aug 19, 12:39 am, Beez <kbiesbr...@gma il.comwrote:

Here's my final effort:

>
I tested this using IE 7.0.5730.11CO and I get ": undefined" for all
three tests.  Is this expected?

Yes, IE doesn't support createEvent. Thanks for testing. :-)


--
Rob

[Beez]

Re: Detecting support for event types

On Aug 18, 10:54 am, RobG <rg...@iinet.ne t.auwrote:

On Aug 19, 12:39 am, Beez <kbiesbr...@gma il.comwrote:
>

Here's my final effort:

>

I tested this using IE 7.0.5730.11CO and I get ": undefined" for all
three tests.  Is this expected?

>
Yes, IE doesn't support createEvent.  Thanks for testing. :-)
>
--
Rob

No problem! Is there an alternative to be had for IE? I looked --
the only thing remotely close that I could find is attachEvent or
fireEvent...nei ther one of which have the same effect.

[dhtml]

Re: Detecting support for event types

RobG wrote:

On Aug 18, 9:26 pm, RobG <rg...@iinet.ne t.auwrote:

>On Aug 18, 4:45 pm, RobG <rg...@iinet.ne t.auwrote:
>>

>>On Aug 18, 12:09 pm, Peter Michaux <petermich...@g mail.comwrote:

I like this type of approach better because it will have faster runtime
performance.

However, if document.create Event is not supported, undefined is
returned. Why not just return true/false?

var hasTouch = (function(){
if (document && document.create Event) {
try {
document.create Event('GestureE vent');
document.create Event('TouchEve nt');
return true;
} catch (e) {
return false;
}
}
})();

Another possible approach would be to create variables for
touch/gesture, so as to avoid a runtime function call. Using the return
true/false approach, we could remove the conditional check altogether.

<!DOCTYPE HTML>
<html>
<head>
<title>EventSup port Demo</title>
<script type='text/javascript'>
var EventSupport = {};
(function(){
var es = EventSupport;
// Initialize the touch and gesture properties.
es.touch = hasSupport("Tou chEvent");
es.gesture = hasSupport("Ges tureEvent");

function hasSupport(s){
try {
document.create Event(s);
return true;
} catch (e) {
return false;
}
}
})();

</script>
</head>
<body>
<pre style="font-size:50px">
<script type='text/javascript'>
document.write(
'EventSupport.t ouch: ' + EventSupport.to uch
+'\nEventSuppor t.gesture: ' + EventSupport.ge sture
)
</script>
</pre>
</body>
</html>


Results:
iPhone 2.0:
EventSupport.to uch: true
EventSupport.ge sture: true

Firefox 3, et c.
EventSupport.to uch: false
EventSupport.ge sture: false


If other events were desired to be known, arbitrarily at runtime,
hasSupport could be added as a property of the EventSupport object.


Garrett

>
--
Rob

[RobG]

Re: Detecting support for event types

On Aug 22, 12:59 pm, dhtml <dhtmlkitc...@g mail.comwrote:

RobG wrote:

On Aug 18, 9:26 pm, RobG <rg...@iinet.ne t.auwrote:

On Aug 18, 4:45 pm, RobG <rg...@iinet.ne t.auwrote:

>

>On Aug 18, 12:09 pm, Peter Michaux <petermich...@g mail.comwrote:

>
I like this type of approach better because it will have faster runtime
performance.
>
However, if document.create Event is not supported, undefined is
returned. Why not just return true/false?

Because touch events might be supported through some other method, I
wanted to distinguish between no support for touch or gesture and no
support for the test itself.

Is that useful, or is true/false all that is required?

>

   var hasTouch = (function(){
     if (document && document.create Event) {
       try {
         document.create Event('GestureE vent');
         document.create Event('TouchEve nt');
         return true;
       } catch (e) {
         return false;
       }
     }
   })();

>
Another possible approach would be to create variables for
touch/gesture, so as to avoid a runtime function call.

Sure, my priority was a test that could be used in whatever manner was
appropriate. For example, when testing code there may be sections
based on mouseover or mouseout. Since touch interfaces don't fire
those events, it's nice to detect touch support and offer buttons to
fire the mouseover/out events if dispatchEvent is also supported.

My testing has been in Mobile Safari on iPhone and it works quite
well, it should be adaptable to other interfaces and perhaps detection
methods.

Other there other touch interfaces that have browsers? I'd be
interested to know how they've implemented DOM 0 events.

Using the return
true/false approach, we could remove the conditional check altogether.

[...]

<script type='text/javascript'>
document.write(
'EventSupport.t ouch: ' + EventSupport.to uch
+'\nEventSuppor t.gesture: ' + EventSupport.ge sture
)
        </script>
</pre>
</body>
</html>
>
Results:
iPhone 2.0:
   EventSupport.to uch: true
   EventSupport.ge sture: true
>
Firefox 3, et c.
   EventSupport.to uch: false
   EventSupport.ge sture: false
>
If other events were desired to be known, arbitrarily at runtime,
hasSupport could be added as a property of the EventSupport object.

I implemented a test page that does almost exactly that :-)


--
Rob