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javajavascriptrhinohost-object

Returning a host object in Rhino


What is the best way to return an host object to JavaScript in Rhino? I have two classes like this:

public class Hosted extends org.mozilla.javascript.ScriptableObject {
    private static final long serialVersionUID = 1;
    public Hosted() {}
    public void jsConstructor() {}

    public String getClassName() {
        return "Hosted";
    }

    public Member jsGet_member() {
        Member m = new Member();
        m.defineFunctionProperties(new String[] { "toString" }, m.getClass(), DONTENUM);
        return m;
    }
}

public class Member extends org.mozilla.javascript.ScriptableObject {
    private static final long serialVersionUID = 2;
    public Member() {}
    public void jsConstructor() {}

    public String getClassName() {
        return "Member";
    }

    public String toString() {
        return "called toString()";
    }
}

It works, in the sense that I can call the toString method, but the member object doesn't behave as I would expect:

js> defineClass("Hosted");
js> defineClass("Member");
js> var h = new Hosted();
js> h.toString();
[object Hosted]
js> h instanceof Hosted;
true
js> h.__proto__;
[object Hosted]
js> 
js> var m = h.member;
js> m.toString();
called toString()
js> m instanceof Member; // Should be true
false
js> m.__proto__; // Should be [object Member]
null

If I call Object.prototype.toString though, it does say it's a Member object:

js> Object.prototype.toString.call(m);
[object Member]

I've tried calling m.setPrototype and Context.javaToJS.


Solution

  •     public Scriptable jsGet_member() {
            Scriptable scope = ScriptableObject.getTopLevelScope(this);
            Member m = new Member();
            m.setParentScope(scope);
            // defineClass("Member") must have previously been called.
            m.setPrototype(ScriptableObject.getClassPrototype(scope, "Member"));
            m.defineFunctionProperties(new String[] { "toString" },
                    m.getClass(), DONTENUM);
            return m;
        }
    

    js> defineClass("Member")
    js> defineClass("Hosted")
    js> var h = new Hosted();
    js> var m = h.member;
    js> m.toString();
    called toString()
    js> m instanceof Member;
    true
    js> m.__proto__;
    [object Member]
    

    Edit: The method can also be written:

        public Scriptable jsGet_member() {
            Scriptable scope = ScriptableObject.getTopLevelScope(this);
            Context cx = Context.getCurrentContext();
            Member m = (Member)cx.newObject(scope, "Member");
            m.defineFunctionProperties(new String[] { "toString" },
                    m.getClass(), DONTENUM);
            return m;
        }
    

    which will call Member.jsConstructor; there may be other differences as well.