?I have something that annoys me about how JavaScript try/catch error
handling currently works. Don't get me wrong, I totally understand why it
works that way, and it makes sense. But having the option to get around that
behavior would be really nice.
My idea/proposal is illustrated with this gist:
https://gist.github.com/802625
Essentially, what I'm running into is several different use-cases for the
need to wrap a try/catch around some call, and "observe" if it error'ed or
not. Notice in the code snippet that I'm "modifying" the error's message
string before re-throwing it. However, that's only one use-case. I might
very well not need to modify the error, but simply passively "observe" (ie,
not interfere with the bubbling up of that error) and for instance do some
sort of cleanup or other graceful handling, and then pass the error along to
continue its bubbling.
The reason for not wanting to interfere is in the sense of wanting the
original error to maintain its original execution context (almost like an
error propagation "stack" if you will), so that when the browser/engine
reports the uncaught error, it reports it from the correct origination point
(source file, line-number, etc).
If you try/catch such an error, and then "re-throw" it, that context is
lost. I'm not positive, but I'm guessing that perhaps this is intentional
by-design, and not just a particular implementation detail. If it *is*
standardized, I'm proposing an alternative/addition. If not, I'm proposing
we standardize a way to both preserve and explicitly not-preserve (aka,
override) the original context. For compat reasons, the default would
certainly stay as it currently is, with my idea being opt-in if the author
needs it.
Of course, JavaScript doesn't expose the internals like the original context
source file/line-number/etc (although I kinda wish it would), so for purely
JavaScript sake it really doesn't matter. But I'm running into this in the
server-side JavaScript world numerous times, and wishing the engine could
keep that context. It's also useful for debugging purposes when looking at
JavaScript errors reported in the browser's error console, for instance.
I'm interested in thoughts on either snippet's approach and the feasibility
of something like this?
--Kyle Simpson
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