My twiddle

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  stableItem: {},
  something: {},
  
  actions: {
    setSomething: function() {
      this.set('something', {});
    }
  }
});

helpers.my-helper.js

import Ember from 'ember';

let count = 0;

export function myHelper([item]) {
  return count++;
}

export default Ember.Helper.helper(myHelper);

templates.application.hbs

<button {{action "setSomething"}}>Set Something</button>
<br>
<br>
{{my-helper stableItem}}
<br>
<br>

twiddle.json

{
  "version": "0.10.5",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "beta",
    "ember-template-compiler": "beta",
    "ember-testing": "beta"
  }
}