KnockoutJS in CoffeeScript

gistfile1.txt

I'm trying to make KnockoutJS's dependentObservables work in CoffeeScript.  See

http://github.com/SteveSanderson/knockout/wiki/Observables

A typical example is:

var viewModel = {
    firstName: ko.observable('Bob'),
    lastName: ko.observable('Smith')
};
viewModel.fullName = ko.dependentObservable(function() {
    return this.firstName() + " " + this.lastName();
}, viewModel);

It's unclear to me how to reproduce this in CoffeeScript.  I'd like to write something like:

class ViewModel
    firstName: ko.observable('Bob')
    firstName: ko.observable('Smith')
    fullName : ko.dependentObservable(=>
        @firstName + " " + lastName

viewmodel = new ViewModel

class ViewModel
firstName: ko.observable 'Bob'
lastName: ko.obserable 'Smith'
fullName: ko.dependentObservable () ->
@firstname + " " + lastName

viewmodel = new ViewModel

That should work, keep in mind that i had to "space" things instead of tabbing