Difference between knockout View Models declared as object literals vs functions

Question

In knockout js I see View Models declared as either:

var viewModel = {
    firstname: ko.observable(\"Bob\")
};

ko.applyBindings(viewModel );

Answer 1

I use a different method, though similar:

var viewModel = (function () {
  var obj = {};
  obj.myVariable = ko.observable();
  obj.myComputed = ko.computed(function () { return "hello" + obj.myVariable() });

  ko.applyBindings(obj);
  return obj;
})();

Couple of reasons:

1. Not using this, which can confusion when used within ko.computeds etc
2. My viewModel is a singleton, I don't need to create multiple instances (i.e. new viewModel())