ArrayProxy Join

controllers.application.js

import Ember from 'ember';
import { A } from '@ember/array';
import ArrayProxy from '@ember/array/proxy';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
    init(...args) {
    	this._super(...args);
      let a = ArrayProxy.create({
        content: A(["hello", "world"])
      });
      console.log(a.join(", ")); 
 	 },
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<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"
  }
}