how to return null from a CLR function exposed to Javascript

[dkottow]

I want to expose a C# function to Javascript that normally returns a number but may also return null (undefined). I have not found a way to handle this, I have tried to convert Undefined to a CommonObject but without success.

I am copying a simple example below. Here we define a function inverse that should return the inverse of a number if not zero, otherwise, undefined:

class Test
{
   IronJS.Hosting.CSharp.Context mContext;

    public Test()
    {
        mContext = new IronJS.Hosting.CSharp.Context();
        var inverse= JSUtils.CreateFunction<Func<double, CommonObject>>(mContext.Environment, 1, inverse);
        mContext.SetGlobal("inv", inverse);

        ret = ctx.Execute("inv(2)"); //returns 0.5
        ret = ctx.Execute("inv(0)"); //Exception  
    }

    CommonObject inverse(double arg)
    {
        if (arg > 0) return TypeConverter.ToObject(mContext.Environment, 1.0 / arg);
        return TypeConverter.ToObject(mContext.Environment, Undefined.Instance); 
    }
}

Any suggestions how this can be done? Thank you

[fholm]

The function to use is TypeConverter.ToBoxedValue(double d), and the IronJS.Runtime.BoxedValue struct. You're trying to convert undefined into an object which is not a valid operation in JavaScript. And boxing is not done with the JS object type, but rather with a special internal type inside IronJS (it's faster, smaller and resides on the stack) called BoxedValue.

Your inverse function should be written like this:

BoxedValue inverse(double arg)
    {
        if (arg > 0) return TypeConverter.ToBoxedValue(1.0 / arg);
        return Undefined.Boxed;
    }

Note that I have not tested this as I don't have access to visual studio on the computer I'm on currently, but it shows you the basics.

[dkottow]

Thank you Frederik,  worked fine.

---

From: Fredrik Holmström reply@reply.github.com To: dkottow dkottowk@yahoo.com Sent: Monday, May 7, 2012 12:22 PM Subject: Re: [IronJS] how to return null from a CLR function exposed to Javascript (#91)

The function to use is TypeConverter.ToBoxedValue(double d), and the IronJS.Runtime.BoxedValue struct. You're trying to convert undefined into an object which is not a valid operation in JavaScript. And boxing is not done with the JS object type, but rather with a special internal type inside IronJS (it's faster, smaller and resides on the stack) called BoxedValue.

Your inverse function should be written like this:

BoxedValue inverse(double arg)
    {
        if (arg > 0) return TypeConverter.ToBoxedValue(1.0 / arg);
        return Undefined.Boxed;
    }

Note that I have not tested this as I don't have access to visual studio on the computer I'm on currently, but it shows you the basics.

---

Reply to this email directly or view it on GitHub: https://github.com/fholm/IronJS/issues/91#issuecomment-5553907