New Twiddle

controllers.application.js

import Ember from 'ember';
import { computed } from '@ember/object';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
  list: [{a: 1}, {a: 2}],
  
  total: 5,
  
  sum: computed('list.[]', {
  	get(){
    	const list = this.get('list');
      
      if(list){
      	return list.mapBy('a').reduce((a,b)=> a + b, 0);
      }
      
      return 0;
    },
    
    set(key,value){
    	return value;
    }
  }),
  
  computed2: computed('list.[]', 'sum', {
  	get () {
    	return this.get('sum') / this.get('total') * 100;
    },
    
    set (key, value) {
      this.set('sum', this.get('total') * (value / 100));

      return value;
    }
  }),
  
	init () {
    this._super(...arguments);
    
    this.set('computed2', 3);
	}
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
<h1>sum: {{sum}}</h1>
<h1>computed2: {{computed2}}</h1>
<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"
  }
}