Subj : Re: evaluateString returns "Undefined"
To   : Anil Atur
From : Igor Bukanov
Date : Thu Jul 29 2004 12:04 pm

Anil Atur wrote:
....
>               Context cx = Context.enter();
>         String test = "Test";
>    6.
>    7.         ScriptableObject scope = cx.initStandardObjects(null, true);
>    8.
>    9.         String script2 =  "function f(x) { return x; }; "
>       +"java.lang.System.out.println(f('"+test+"'));";
>   10.
>   11.         Scriptable threadScope = cx.newObject(scope);
>   12.
>   13.   Object result  =   cx.evaluateString(threadScope, script2,
>       "Test", 1, null);
>   14.
>   15.   String report = cx.toString(result);
>   16.
>   17.   System.out.println("report : " + report);
>   18.
>   19.     }
>   20.
>   21. }
>   22.
>   23.    
> 
>                 Line Number 15 outputs a string as UNDEFINED ..
>  
>                 The evaluateString evaluates the function f() and 
> displays the output as 'Test' from the *script2* . The return object is 
> the result and when converted to a  string *cx.toString(result)* 
> displays as "*Undefined*" .. How do we go about this ..??

In your program you evaluates the script:

function f(x) { return x; };java.lang.System.out.println(f('Test'));

Its result should be the result of the last statement which is
java.lang.System.out.println(f('Test'));

Since System.println in Java returns void, Rhino translates that into 
undefined object. When you later call cx.toString(result) that will 
convert that to string and give "undefined" according t the rules of 
JavaScript.

BTW, you omitted Context.exit() call from your program, you MUST always 
use the pattern:

Context cx = Context.enter();
try {
     Code that use cx
} finally {
     Context.exit();
}

Otherwise at best you get memory leak and at worst you end up with 
potential RuntimeException.

Another problem is the line:

Scriptable threadScope = cx.newObject(scope);

If you want to follow  http://www.mozilla.org/rhino/scopes.html , then 
you should do after the call:

threadScope.setPrototype(scope);
threadScope.setParentScope(null);

Otherwise you are effectively execute your scripts as in:

with(threadScope) {
    your script
}

In this way all variables declared in the script will be stored not in 
threadScope, but rather in the original global scope returned by 
cx.initStandardObjects() and your threadScope would be pretty much ignored.

Regards, Igor

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