Custom JavaScript object wrapping SOAP calls

Hi.  I'm writing some javascript object wrappers so that I can use either 
Mozilla or IE (and its webservice behavior) with my existing app to access 
some web services from the browser.  In particular, I'm dealing with 
asynchronous invocation.  I can successfully call the remote method, but I'm 
having trouble designing a good generic callback mechanism, since the 
argument lists are different between the Mozilla way and the IE 
webservice.htc way.

I'd like to do something like this...

var mycall = new MyCallWrapper("RemoteMethodName", myparamarray);
mycall.execute(mycallback);

...and have mycallback be called on return of the remote method.  Here's the 
idea of the MyCallWrapper class...

function MyCallWrapper(methodname, parameters) {
    this.method = methodname;
    this.params = parameters;
    this.call = new SOAPCall();
    // set info on the call object...
}
MyCallWrapper.prototype.execute = function (callback) {
    this.callback = callback;
    this.call.asyncInvoke(this.genericCallback);
}
MyCallWrapper.prototype.genericCallback = function (response, call, error) {
    // manip results into compatible forms between IE and Mozilla, then..
    this.callback(genericresponse, genericerror);
}

...but this doesn't work.  My genericCallback gets called after I run 
mycall.execute(), but then this.callback is always undefined.  I guess I'm 
not really getting the genericCallback called on the same instance of 
MyCallWrapper as I invoked the method on.  I think this is weird, but I'm 
not a javascript expert.  How can I get my generic callback function to call 
my "real" callback function?

Also, if a different model would be more appropriate, I'm open to 
suggestions!


thanks,
Chris