property readOnly

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
  data: function() {
    return [1, 2, 3, 4, 5];
   }.property().readOnly()
  
  , actions: {
    change() {
      this.set('data', [1, 2, 3]);
    }
  }
});

// http://emberjs.com/api/classes/Ember.computed.html
// http://emberjs.com/api/classes/Ember.ComputedProperty.html
// http://emberjs.com/api/classes/Ember.computed.html#method_readOnly

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
{{data}}

<button {{action 'change' }}>Change</button>
<br>
{{outlet}}
<br>
<br>

twiddle.json

{
  "version": "0.10.6",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.9.0",
    "ember-data": "2.9.0",
    "ember-template-compiler": "2.9.0",
    "ember-testing": "2.9.0"
  },
  "addons": {}
}