Inconsistent missing property handling with java objects

Bullotta, Rick rick.bullotta at
Wed Sep 3 15:34:15 UTC 2014

Also, since you can theoretically extend the Java object (I think?) in Nashorn with dynamic properties, how could the runtime know that the missing property was a missing "built in" property/method on the object or a not-yet-or-never added property on the dynamic object?

-----Original Message-----
From: nashorn-dev [mailto:nashorn-dev-bounces at] On Behalf Of Mike Rettig
Sent: Wednesday, September 03, 2014 11:30 AM
To: Hannes Wallnoefer
Cc: nashorn-dev at
Subject: Re: Inconsistent missing property handling with java objects

There are a couple reasons why it is problematic for me. The java objects are not dynamic objects. The interface is static. Allowing silent failures leads to all sorts of time consuming and frustrating bugs. Nashorn doesn't wrap the java objects, so it should treat them like java objects.
Referencing an unknown property on a java object should fail (as it did in Rhino). The current behavior is the worst of both worlds. The java object is not wrapped so there are no extension points (e.g. __noSuchProperty___), but in the case of a missing property it behaves like a js object by silently failing.

Anyone know the reasoning behind this design decision?



On Wed, Sep 3, 2014 at 10:00 AM, Hannes Wallnoefer < hannes.wallnoefer at> wrote:

> Hi Mike,
> It was just a design decision to handle missing Java properties this 
> way in Nashorn.
> The behaviour is implemented in NashornBottomLinker.linkBean method.
> Unfortunately there's currently no way to configure Nashorn to behave 
> the way you want it to.
> Regards,
> Hannes
> Am 2014-09-03 um 16:13 schrieb Mike Rettig:
>  With nashorn, it seems that the assignment and accessing of missing
>> properties on java objects is handled as 'undefined'.
>> Example:
>>          String engine = "nashorn";
>>          ScriptEngineManager engineManager =
>>                  new ScriptEngineManager();
>>          final ScriptEngine nashorn = engineManager.getEngineByName( 
>> engine);
>>          nashorn.eval("var d=new java.util.Date();");
>>          nashorn.eval("d.badProp=1233");
>>          nashorn.eval("print(d.badProp)");
>> This will print 'undefined'. It doesn't fail on the 'badProp' on the 
>> Date object. With Rhino, this would fail on the assignment of the bad 
>> property with the following error:
>> "Exception in thread "main" javax.script.ScriptException:
>> Java class 
>> "java.util.Date" has no public instance field or method named "badProp".
>> (<Unknown source>#1) in <Unknown source> at line number 1"
>> I want the script to fail when the bad property is referenced.  I've 
>> tried 'use strict', the rhino compatibility script, and attempting to 
>> define __noSuchProperty__ on the java object. I can create a wrapper 
>> object that simply delegates to the java object and throws if a 
>> property is undefined, but that seems excessive.
>> Is this the correct behavior? Is there a way to work around this 
>> behavior in nashorn?
>> Thanks,
>> Mike

More information about the nashorn-dev mailing list