SameProp

controllers.application.js

import Ember from 'ember';
import { set } from '@ember/object';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  someObj: { a: 1 },
  init() {
		this._super(...arguments);
    this.someProp = this.someObj;
  },
  
  actions: {
    changeSomeProp() {
      set(this, 'someProp.a', 2);
    },
  },
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
Some Obj a: {{someObj.a}}
<br>
Some Prop a: {{someProp.a}}
<br>
  <button {{action 'changeSomeProp'}}>Clicking on the button will change both props!</button>
<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"
  }
}