New Twiddle

components.my-component.js

import Ember from 'ember';

export default Ember.Component.extend({
  things: ['one', 'two', 'three'],
  thing: null,
  
  init(){
  	this._super(...arguments);
    this.addObserver('things.length', function(){console.log(this.things)})
  },
  
  actions{
    addThing(thing){
      this.things.push(thing);
      this.set(thing, null);
    }
  }
});

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}}
<br>
<br>

templates.components.my-component.hbs

<ul>
{{#each things as |thing|}}
<li>{{thing}}</li>
{{/each}}
</ul>

{{input value=thing}} 
<button {{action 'addThing' thing}}>ADD</button>

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"
  }
}