RE: SomethingEventInit dictionaries

> From: Martin Thomson []
> The draft currently includes an interesting pattern (thanks Yang for
> inadvertently reminding me of this) for declaration of Event classes.
> It goes like this:
> [Constructor(SomethingEventInit data)]
> interface SomethingEvent : Event {
>     readonly attribute Something attr;
> }
> dictionary SomethingEventInit {
>     Something attr;
> }
> After having actually implemented most of this stuff, most of the time it
> is sufficient (in JavaScript at least) to instantiate Event and tack the
> necessary attributes on.  Even in a formal sense, the SomethingEventInit
> object has no need to be in the public namespace, let alone the
> specification.  I can understand why the internals of your implementation
> might use these, but are really just browser internals.  Applications
> don't need either definition.  Why isn't the pattern like so?

It's not quite just browser internals. The constructable Event is exposed as an object to script as:


so that new SomethingEvent() can be called on it and dispatched with object.dispatchEvent().

However, what's missing above is the inheritance of the dictionary. It should be:

dictionary SomethingEventInit : EventInit

This lets you assign values to all the readonly attributes on the regular event and/or other derived classes.

Received on Friday, 19 October 2012 05:14:17 UTC