Le 19/12/2012 14:13, Claude Pache a écrit :
Hello,
In SpiderMonkey (and perhaps other JS engines?), there are conditional catch
clauses:
catch (exception if condition)
Could such a feature added to ECMAScript?
Rationale: Although try/catch mechanism was initially intended for treating
errors, it could be used in normal control flow with non-error condition.
Why not just use normal control flow when you want to express non-error
conditions?
throw/try/catch was indeed intented for treating errors and when I read
code, I expect an error path when encountering a try/catch.
ES.next sanction this pattern with StopIteration. In this case, it would be
nice to have a catch clause listening only what is wanted, without having to
add code for filtering out and rethrowing. Here is an example of use:
Map.prototype.some = function(f, o) {
var ok = {} // an arbitrary private object
try {
this.forEach(function(v, k, m) {
if (f.call(o, v, k, m))
throw ok
})
}
catch (e if e === ok) {
return true
}
return false
}
instead of, e.g.,
catch (e) {
if (e !== ok)
throw e
return true
}
I don't see the benefit from your example. You're basically removing one
or 2 lines of code in an hardly more expressive way. Your above example
could even be rewritten as:
catch (e) { if (e !== ok) throw e
return true
}
That could be a code convention without needing to be part of the language.
Do you have example of code in the wild that would benefit (performance,
readability, etc.) from such an addition?
David
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