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Re: Detecting and Creating Events

From: Garrett Smith <dhtmlkitchen@gmail.com>
Date: Wed, 26 Aug 2009 00:58:01 -0700
Message-ID: <c9e12660908260058l141bf23ew7c9566e463df4cf2@mail.gmail.com>
To: Doug Schepers <schepers@w3.org>
Cc: DOM mailing list <www-dom@w3.org>
On Tue, Aug 25, 2009 at 1:11 AM, Doug Schepers<schepers@w3.org> wrote:
> Hi, Garrett-
>
> Thanks for your proposal.  I don't believe we'll add this in the DOM3 Events
> spec, since we are trying to get it out the door, but continued discussion
> about it is helpful, and we may consider this for some later spec.
>

Don't ship shit.

Regards,

Garrett

> Regards-
> -Doug Schepers
> W3C Team Contact, SVG and WebApps WGs
>
>
> Garrett Smith wrote (on 8/20/09 1:18 AM):
>>
>> The inability to easily and accurately detect events is a problem.
>> Programs want to know if an event is implemented at runtime. If it is,
>> then the feature can be used. If not, it a fallback stratety is in
>> order. Many new event types are being created and implemented. How can
>> a program feature-test to see if they are implemented?
>>
>> Proposal: add a "hasEvent" method to EventTarget:
>>
>> EventTarget {
>>   boolean hasEvent(in DOMString eventType)
>> }
>>
>> This allows script to call the target's "hasEvent" method to see if
>> the event is (claimed to be) supported.
>>
>> var hasFocusIn = false;
>>
>> if(typeof el.hasEvent != "undefined") {
>>   hasFocusIn = el.hasEvent("domfocusin");
>> }
>>
>> A potential complication would be - hasEvent("domfocusin") - returns
>> true, but the event handler does not fire as expected/specified, or
>> vice versa. Consider if the "hasEvent" inference check fails and this
>> failure is discovered in a browser. The program would need to be
>> amended so that it could detect the event where actually implemented,
>> not where - hasEvent - returns true. The program can create and
>> dispatch the event, setting a "fired" flag in the callback.
>>
>> There should be a simple way to create and fire an event.
>>
>> interface DocumentEvent {
>>   Event createInitedEvent(in domstring type, in Object options)
>>   raises(dom::DOMException);
>> }
>>
>> In createInitedEvent, the type of event created is determined by the
>> string arg /type/, which is a prefixed with a DOM Interface (as a
>> string) followed by ".", followed by the event type. The event is
>> inited with the /options/. This is a "map" of options that the event
>> has, such as - offsetX - , - pageY - , etc.
>>
>> The keys in /options/ depend on the event type. An option that is
>> unrecognized for a particular event type would be ignored. This is
>> important for extensibility -- new options may be possible in the
>> future.
>>
>> The values and their types for each property/key in options is
>> constrained by the interface for the type of event. So, for example,
>> for a "click", an option - shiftKey -, - metaKey -, ctrlKey - would
>> require a boolean value, while - button - would require a dom unsigned
>> short. Options that are required but missing would get a default
>> value, so, for example:-
>>
>> document.createInitedEvent("MouseEvent.click", null);
>>
>> - would return a MouseEvent that, when dispatched on a target, would
>> have the following properties:-
>>
>>   screenX : 0
>>   screenY : 0
>>   clientX : 0
>>   clientY : 0
>>   ctrlKey : false
>>   shiftKey : false
>>   altKey : false
>>   metaKey : false
>>   button : 0
>>
>> Future versions of the API can be modified to have new types of events
>> and new options for existing events. These modifications can be
>> feature tested by a script running in a browser, so, if a browser
>> added a "progress" event to an object, and the program wanted to know
>> if it (a) "progress" was implemented on that object and (b) that event
>> has a "data" property, it would be able to make a feature check to
>> make such determination.
>>
>> DOM 2 Events provides "createEvent(type)", but then required an
>> additional step initEvent or initMouseEvent. Method initMouseEvent
>> takes 15 arguments, none of them are memorable. It is painful to use.
>>
>> With createInitedEvent, the following would be possible:-
>>
>> function isFocusInSupported(){
>>   var hasFocusIn = false;
>>
>>   if(typeof document.dispatchEvent != "undefined"&&
>>     typeof document.createInitedEvent != "undefined") {
>>     try {
>>       var fev = document.createInitedEvent("UIEvent.domfocusin", null),
>>           n = document.documentElement,
>>           ti = n.tabIndex;
>>       n.tabIndex = "0";
>>       if(n.dispatchEvent) {
>>         n.addEventListener("focus", gotFocus, false);
>>         n.dispatchEvent(fev);
>>       }
>>     } catch(ex) {
>>       if(ti) {
>>         n.tabIndex = ti;
>>       }
>>       n.removeEventListener("focus", gotFocus, false);
>>     }
>>   }
>>   return hasFocusIn;
>> }
>> function gotFocus(ev) {
>>   hasFocusIn = true;
>> }
>>
>> (This assumes that callbacks fire synchronously, as they currently
>> seem to do in browsers. )
>>
>> The proposed features are fully feature-testable, and so partially
>> backwards-compatible (failing with false negatives). Browsers that
>> don't support the new methods won't get there. It allows applications
>> to be forwards-compatible by providing the ability to check to see if
>> an event will fire.
>>
>> isFocusInSupported();
>>
>> Result: false
>>
>> Garrett
>>
>>
>
Received on Wednesday, 26 August 2009 07:58:41 GMT

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