index.jade

form(data-bind='submit: loadFoobar')
  button(type='submit', data-bind='css: { loading: loadFoobar.loading }')

viewModel.coffee

class ViewModel
  constructor: ->
    @loadFoobar.loading = ko.observable false
    
  loadFoobar: ->
    @loadFoobar.loading true
    
    makeAjaxRequest =>
      @loadFoobar.loading false