Rails json view into javascript function

I am storing some json data in an active-record session so have created a route and controller action which renders fine in the browser but when I try and pass the route into a JavaScript function the response in browser(chrome) network tab is null

Controller

class DataFilesController < ApplicationController
  def show
    render json: session[:my_data]
  end
end

Route

get 'data-file.json', to: 'data_files#show', as: :data_file

Javascript function (in view)

= content_for :javascript do
  :javascript
    accessibleAutocomplete({
      element: document.querySelector('#autocomplete-wrapper'),
      id: 'autocomplete',
      source: openregisterPickerEngine({
        url: "<%= data_file_path %>"
      }),
      templates: {
        inputValue: inputValueTemplate,
        suggestion: suggestionTemplate
      }
    });