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.
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
}
It is arguably not an important feature, but it is a nice one. Note also that
the "if condition" construct is the same as in array comprehension (I want to
say: it is not "yet another syntax").
Claude
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