New Twiddle

components.my-component.js

import Ember from 'ember';

export default Ember.Component.extend({
  test: "no",
  init(){
    this._super(...arguments)
    this.set("test2", "hi2")
  },
  didReceiveAttrs(){
    console.log(this.test)
  }
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle'
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
<MyComponent @test="hi"/> 
<br>
<br>

templates.components.my-component.hbs

{{@test}}
{{test}}

{{@test2}}
{{test2}}

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"
  }
}