Question

I’ve been looking at the Rhino documentation and source code for a clue as to how to implement my own global native function. This task is however more complicated than I expected it to be.

After reading the code of the implementation of the require function in RingoJS I believe I need to do something along the following lines:

import org.mozilla.javascript.BaseFunction;
import org.mozilla.javascript.Scriptable;
import org.mozilla.javascript.Context;

public class MyGlobalNativeFunction extends BaseFunction {
    public MyGlobalNativeFunction() {}

    public Object call(Context cx, Scriptable scope, Scriptable thisObj, Object[] args) {
        // implementation of my function
    }

    public int getArity() {
        return 1;
    }
}

Am I on the correct track? A step by step walkthrough on how to achieve this would be great.

Also it would be great if I could use Rhino’s defineClass function to create my global native function. I’m not too keen on rolling out my own modified version of Rhino just because I want to implement one native function.

Answer 1

I think this should work, and if you only want to implement a single global function it’s a good approach. If you want to implement multiple functions or a host object, there are other approaches.

You’d then use something like this to instantiate your function:

scope.defineProperty("myNativeFunction",
                     new MyGlobalNativeFunction(),
                     ScriptableObject.DONTENUM);

Check out RingoGlobal for how this is done (it also shows how to define multiple functions in one sweep without having to creating a class for each). The Rhino examples directory contains some examples of how to create proper host objects with Rhino.