HI Sundar -
On 20/02/15 08:09, A. Sundararajan wrote:
* SyntaxError constructor accepting extra arguments apart from message
is not as per ECMAScript standard. That one is Firefox/Mozilla
specific extension. We try to *add* properties, functions for
extension - try not to modify/extend standard defined functions,
constructors.
* User can fileName, lineNumber and columnNumber of constructed
SyntaxError instance.
* On the java side, the NashornException and ScriptException's file,
line, column use the actual throw point from the script source. While
this can read the values from SyntaxError or any Error for that
matter, there is a problem. fileName, lineNumber, columnNumber could
be set to any value in script. These have to be converted to String,
int, int respectively. Conversion means calling [[DefaultValue]] with
String, Number hint - which is calling out to script code. This
process can itself throw exception!! All this may destroy info. on
where exactly the underlying exception was thrown.
* There is clear workaround. Script code can always read SyntaxError
instance's fileName, lineNumber etc. - which can be set to anything
post construction. Java code can get underling ECMA error instance via
NashornException.getEcmaError - which would return a
ScriptObjectMirror. Java code can call
ScriptObjectMirror.getMember("fileName") etc. to retrieve properties
set by user's script.
I've tried what you suggest, it seems to work (ish), but I end up with
seriously grungy code that relies on casting and non public APIs that (I
guess) could be changed without warning in any release, so I don't think
I'd be happy doing this in Vert.x. Here's an example:
(Yikes!)
https://gist.github.com/purplefox/003fae1e32fd44368ffa
So.... rewinding a bit here. The only reason I find myself shaving this
particular Yak is because syntax errors thrown from evals() aren't
reported by Nashorn with the fileName and lineNumber of the _eval_,
instead they are reported with the fileName/lineNumber of where the eval
was executed.
I mentioned this in a previous post, but here is the gist again that
demonstrates the issue:
https://gist.github.com/purplefox/7ba0d87d2d1670b871a4
This means I have to manually catch SyntaxErrors in our require()
implementation. Fill in the correct fileName, lineNumber etc and rethrow
as new SyntaxError instances. But, as we discussed in this thread, that
doesn't seem to work easily as I can't set fileName, lineNumber etc when
constructing an instance in Nashorn, and if I set it afterwards those
values aren't visible in Java (at least not in a portable way that
doesn't rely on hacky reliance on non public APIs). If I don't do this,
our users see a pretty useless error message when there's a syntax error
in their module and it all leads to a very poor user experience.
Imho, a better way to solve this would be for Nashorn to create syntax
error instances when doing evals() that properly reflect the lineNumber
and fileName of the _eval_ not of the place the eval was executed. This
seems a far more intuitive way to do it and it would be consistent with
the way other Error types are thrown from code in evals (e.g. TypeError,
RangeError etc) which *do* reflect the correct line in the eval where
the error occurred. Fundamentally a user is not going to care about the
lineNumber where the eval was executed, they want to know where in the
actual code the syntax error is - that's the useful information which is
currently being obscured.
So, any chance of changing/fixing the current behaviour? Doing that
would mean I wouldn't have to little our code with piles of Yak hair
trying to get the important information out of private classes, and I
think it would lead to a better and more intuitive user experience :)
Hope this helps,
-Sundar
On Wednesday 18 February 2015 08:29 PM, Tim Fox wrote:
Hi all,
I've started a new thread for this, so as not to clutter the previous
thread on exceptions.
I've come across a possible issue with creating SyntaxError objects
(and potentially other exceptions although I haven't tested them).
https://gist.github.com/purplefox/dfe30a38098c1708e24b
In the above gist I create a SyntaxError specifying message,
fileName, and lineNumber.
However fileName and lineNumber appear to be ignored, and instead the
SyntaxError fileName and lineNumber are set to the fileName of the
file where it was created and the lineNumber of the creation.
I'm not sure if I'm doing something wrong, but according to
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SyntaxError
I should be able to create SyntaxError objects like this.
There appears to be a further issue. If I then throw the syntax error
from the JS script, and catch it in Java like this:
try {
engine.eval(script);
} catch (ScriptException e) {
System.out.println("message:" + e.getMessage());
System.out.println("fileName:" + e.getFileName());
System.out.println("lineNumber:" + e.getLineNumber());
}
Then the message, fileName and lineNumber always correspond to place
where the object was created, not to the subsequently set values.
In other words, I can't figure out a way of creating a SyntaxError
object in JS with my own values of fileName and lineNumber and have
those values available in Java when caught.
Any ideas from the experts? :)
