Ember get set

controllers.application\.js

import Controller from '@ember/controller';
import object, { set } from '@ember/object';

export default Controller.extend({
  
  canShowUpgradeBanner: false,
  
  init(){
    
    this._super(...arguments);
    
    let self = this;

    // set(self, 'canShowUpgradeBanner', window.localStorage.getItem('canShowUpgradeBanner') ? window.localStorage.getItem('canShowUpgradeBanner') : window.localStorage.setItem('canShowUpgradeBanner', self.canShowUpgradeBanner));
  }
});

templates.application\.hbs

<h1>Ember Get/ Set</h1>
<br>
<br>

{{canShowUpgradeBanner}}

{{outlet}}
<br>
<br>

twiddle\.json

{
  "version": "0.17.1",
  "EmberENV": {
    "FEATURES": {},
    "_TEMPLATE_ONLY_GLIMMER_COMPONENTS": false,
    "_APPLICATION_TEMPLATE_WRAPPER": true,
    "_JQUERY_INTEGRATION": true
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.js",
    "ember": "3.18.1",
    "ember-template-compiler": "3.18.1",
    "ember-testing": "3.18.1"
  },
  "addons": {
    "@glimmer/component": "1.0.0"
  }
}