Problem with interoperability with JavaFX WebEngine

[A. Sundararajan]

I think I found the issue with this modified script.

var WebEngine = Java.type("javafx.scene.web.WebEngine");
var engine = new WebEngine();

var window = engine.executeScript("window");

print(Debug.getClass(window.foo));
print("typeof(window.foo) = " + typeof(window.foo));
if (window.foo) {
     print("window.foo is truthy");
}

We need to run with -J-Dnashorn.debug to enable nashorn debug mode. 
Debug.getClass gets the Java class of the value. Apparently, browser's 
JSObject impl. returns a string with the value "undefined" for undefined 
values! And not a special value or null for undefined...

I think nashorn's BrowserJSObjectLinker has to probably call 
JSObject.hasMember to check existence of a member before calling 
JSObject.getMember. That appears to be the only way to find out if 
"undefined" string is due to missing property or not.

-Sundar

On Friday 27 March 2015 06:22 PM, A. Sundararajan wrote:
> Browser's DOM objects (like WebEngine's) implement 
> netscape.javascript.JSObject interface. Such objects are treated 
> specially by nashorn's linker.
>
> http://hg.openjdk.java.net/jdk9/dev/nashorn/file/ca150ddd536e/src/jdk.scripting.nashorn/share/classes/jdk/nashorn/internal/runtime/linker/BrowserJSObjectLinker.java 
>
>
> is the dynalink linker that handles such objects. JSObject.getMember, 
> putMember, call are used to provide property, call access seamlessly.
>
> Please check out this example:
>
> http://hg.openjdk.java.net/jdk9/dev/nashorn/file/ca150ddd536e/samples/browser_dom.js 
>
>
> So, what you're seeing is a bug in the way that linker works.  Let me 
> check out and file a bug.
>
> Thanks,
> -Sundar
>
>
> On Friday 27 March 2015 04:41 PM, David P. Caldwell wrote:
>> So it's very cool, and unexpected, that JavaScript objects obtained
>> from a JavaFX WebEngine show up as something like ordinary Nashorn
>> objects in Nashorn scripts. That's an unexpected bonus (I was planning
>> on using .setMember() and all that stuff from
>> netscape.javascript.JSObject).
>>
>> The objects behave a bit strangely, though. So I've got a couple of
>> bug reports, I guess.
>>
>> Here's a script that demonstrates the ones I've found so far:
>>
>> var WebEngine = Java.type("javafx.scene.web.WebEngine");
>> var engine = new WebEngine();
>>
>> var window = engine.executeScript("window");
>>
>> print("foo = " + window.foo);
>> print("typeof(window.foo) = " + typeof(window.foo));
>> if (window.foo) {
>>      print("window.foo is truthy");
>> }
>>
>> Output:
>> $ /usr/lib/jvm/jdk1.8.0_40/bin/jjs -fx nashorn.js
>> foo = undefined
>> typeof(window.foo) = string
>> window.foo is truthy
>>
>> I actually am using a much more complicated embedding that is done
>> from Java, so I can tell you the problem is not in the implementation
>> of the -fx flag.
>>
>> Other than that, I can't see much; I haven't delved into the Nashorn
>> code, let alone whatever magic enables this.
>>
>> -- David.
>