Cannot find my mistake with jQuery autocomplete and Rails 4

router

  resources :pcps  do
    collection do
      get 'autocomplete'
    end
  end

controller

def autocomplete
    @pcps = Pcp.order(:last).where("last like ?", "%#{params[:term]}%")
    render json: @pcps.map(&:full_name)
end

View

= f.text_field :pcp, data: {autocomplete_source:  '/pcps/autocomplete'}

Coffee script

This code works

jQuery ->
  $('#sched_pcp').autocomplete
    source: ["Atest", "Btest","Ctest","Dtest","Btest1","Btest2"]

This code does not work.

jQuery ->
  $('#sched_pcp').autocomplete
    source: $('#sched_pcp').data('autocomplete-source')

I am using ruby 2.2 and rails 4.2 The url '/pcps/autocomplete' returns the correct data. Can someone help me see my mistake please? or maybe give me an idea how to debug it.