A few questions and suggestions.

[Brendan Eich]

On Apr 29, 2007, at 8:24 PM, Michael Daumling wrote:

> Hi Thiago,
>
> Just a quick word about this:
>
>>> *** Exceptions
>>>
>>> Currently, I really miss the ability to catch exceptions given it's
> type. In the new ES spec, will the following code be possible?
>
>>> Try {  ... }
>>> catch(e : TypeError) {  ... }
>>> catch(e : ReferenceError) {  ... }
>
> The correct syntax is in today's SpiderMonkey implementation already,
> and it goes like this:
>
> try {...}
> catch (e if e instanceof TypeError) { ... }
>
> In short: JavaScript supports conditional catches, and you can, of
> course, check the type of an error this way.

Actually, that's a SpiderMonkey extension proposed for ES3 and  
rejected. We favored it instead of what ES3 forces you to do:

   try { ... }
   catch (e) {
     if (guard1) ...
     else if (guard2) ...
     ...
     else if (guardN) ...
     else throw e
   }

where the guardN expressions involve e somehow. We observed that it's  
easy to forget to rethrow on mismatch.

ES4 has catch (e : type) ... clauses, as Thiago wants.

/be

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