[e-lang] E-on-JavaScript property mapping: fail on nonexistence?

[Mark Miller]

On Sun, Aug 23, 2009 at 1:12 PM, David-Sarah Hopwood <
david-sarah at jacaranda.org> wrote:

> Kevin Reid wrote:
> > In E-on-JavaScript, when in Cajita mode, object["foo"] accesses the
> > foo property of object. Should it throw if the property does not
> > exist,
>
> Yes. It's E-on-JavaScript, so E's philosophy about avoiding silent
> failures applies.


I agree.


> Cajita would throw if not for the constraint of
> being a fail-stop subset of ECMAScript.


Actually, that would be allowed within the definition of fail stop. However,
we don't because the "feature testing" pattern -- "if (foo.bar) {
foo.bar(...); }" is way too common, and, like a failed side effect, a read
resulting in an undefined is likely to be noticed. This is the same reason
that ES5-strict chose not to throw for failed reads but does throw for many
other failures.

-- 
Text by me above is hereby placed in the public domain

   Cheers,
   --MarkM
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