changing service property and accessing it globally

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  name1: null,
  name2: null,
  init() {
    this._super(...arguments);
    // print initial value
    this.set('name1', (this.get('serviceName').name)); // hello
    // change value of name property in service
    this.get('serviceName').changeName("hai");
    // print changed value
    this.set('name2', (this.get('serviceName').name)); // hai
  }
});

initializers.inject-service-name.js

export function initialize(application) {
  application.inject('controller', 'serviceName', 'service:service-name');
  // if needed
  application.inject('route', 'serviceName', 'service:service-name');
  application.inject('component', 'serviceName', 'service:service-name');
}

export default {
  initialize
};

services.service-name.js

import Ember from 'ember';

export default Ember.Service.extend({
  name: "hello",
  changeName(name) {
    this.set('name', name);
  }
});

templates.application.hbs

<h1>before change</h1> {{name1}}
<h1>after change</h1> {{name2}}

<br>
<br>
{{outlet}}
<br>
<br>

twiddle.json

{
  "version": "0.15.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.4.3",
    "ember-template-compiler": "3.4.3",
    "ember-testing": "3.4.3"
  },
  "addons": {
    "ember-data": "3.4.2"
  }
}