Create C# class with constructor that acts as expando

Question

I'm wondering is it possible to create a class that acts just Like ActiveXObject in earlier IE version and pass it over to MS ClearScript? I've found a piece of code that creates an instances of ActiveXObjects with their string name.

class ActiveXObject 
{
  public ActiveXObject(string progID)
    {
        try
        {
            dynamic wshShell = Activator.CreateInstance(Type.GetTypeFromProgID(progID));
            
        }
        catch
        {
            return null;
        }
    }
}

Here's the code to attach a c# object to MS ClearScript Object

using (var engines = new V8ScriptEngine())
{
  engines.AddHostObject("ActiveXObject", new ActiveXObject());
}

the only problem is how to assign wshshell to the instance of the class? It's for educational purposes btw.

score 1 · Accepted Answer · answered Jan 01 '21 at 22:54

If you implement ActiveXObject as a JavaScript constructor, it can return an arbitrary object. It can't return null in case of failure, but you can work around that:

dynamic setup = engine.Evaluate(@"
    (function (factory) {
        ActiveXObject = function (progID) {
            return factory(progID) ?? { valueOf: () => null };
        }
    })
");
Func<string, object> factory = progID => {
    try {
        return Activator.CreateInstance(Type.GetTypeFromProgID(progID));
    }
    catch {
        return null;
    }
};
setup(factory);

Now you can do things like this:

engine.AddHostType(typeof(Console));
engine.Execute(@"
    let fso = new ActiveXObject('Scripting.FileSystemObject');
    if (fso.valueOf()) {
        for (let drive of fso.Drives) {
            Console.WriteLine(drive.Path);
        }
    }
");

Note that the original ActiveXObject didn't return null in failure cases either; it threw exceptions.

Create C# class with constructor that acts as expando

1 Answers1