New Twiddle

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  items: Ember.computed(function(){
  	let items = [{name: 'foo'},{name: 'boo'}];
    return Ember.A(items);
  }),
  actions: {
  	replaceFirstObject() {
     	this.items.replace(1, 1, [{ name: Math.random() }]);
    }
  }
});

templates.application.hbs

<button {{action 'replaceFirstObject'}}>replace</button>
<ul>
{{#each this.items as |item|}}
	<li>{{item.name}}</li>
{{/each}}
</ul>

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"
  }
}