New Twiddle

components.my-component.js

import Ember from 'ember';

export default Ember.Component.extend({
  actions: {
   	mutate() {
    	this.set('items', [1,2,3]);
    } 
  }
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  items: [1]
});

templates.application.hbs

{{#each this.items as |item|}}
	{{item}}
{{/each}}

{{my-component items=this.items}}

templates.components.my-component.hbs

<button type="button" {{action 'mutate'}}>Change items</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"
  }
}