Pros:
* Fits the object-oriented programming model of "new Image", "new
XMLHttpRequest", etc.
* Enables use of object-oriented features like instanceof,
the .constructor property, and prototype-based extensions to timer
objects.
* Distinguishes itself better from the old setTimeout / setInterval
functions.
In general, the DOM does not depend on a constructor as the only way
to create a kind of object, since it is nominally language-agnostic.
In fact, for most things it doesn't provide a constructor invokable
as such at all; you listed some of the few exceptions.
A Timer constructor is language-agnostic as long as you specify that
"new Timer()" and "Timer()" behave the same way. Other JavaScript
constructor APIs, like Array, behave this way.
The fact that most things in the DOM aren't instantiated by
constructors is really just an accidental consequence of the fact that
they're available as properties of the document, and it makes no sense
to create them standalone. The two qualities are not found in timers.
In addition, "new Timer(...)" does not as clearly express the fact
that the timer is not only created but started right away. So I
don't think a constructor would be good as the sole interface for
starting a timer.
That seems like a minor criticism, relative to the pros above.
Besides, we all know that if this API becomes standardized, Mozilla is
going to add a global Timer constructor, just like they did for all
the other classes in the DOM. And we all know that WebKit will follow
suit. So why not get a jump start on things, and specify it that way
from the beginning?
I guess we could make a Timer constructor that threw when you called
it, as we did with node-related DOM constructors, but that behavior is
really weird.
Geoff
