Plugin template helper

In my discourse plugin's folder discourse-adplugin/assets/discourse/helpers/ I've created a file with helper discourse-adplugin/assets/discourse/helpers/eq.js.es6:

import { registerHelper } from 'discourse/lib/helpers';

var makeBoundHelper = Ember.HTMLBars.makeBoundHelper;

registerHelper('insert_ad', makeBoundHelper(function(params) {
  var dfp_top_3_display = Discourse.SiteSettings.dfp_top_3_display;

  if (dfp_top_3_display < 0) return false;

  return params[0] == dfp_top_3_display;
}))

I'm using this helper in template, in development environment it works well but it doesn't work in docker production, it produces the error:

Uncaught Error: Could not find module 'discourse/lib/helpers' imported from 'discourse/plugins/discourse-adplugin/discourse/helpers/eq'

What is the right way to create template helpers in plugin?