New Twiddle

controllers.application\.js

import { A } from '@ember/array';
import EmberObject, { computed } from '@ember/object';
import Controller from '@ember/controller';

export default Controller.extend({
  todos: null,

  init() {
    this._super(...arguments);
    this.set('todos', A([
      EmberObject.create({ title: 'A', isDone: true }),
      EmberObject.create({ title: 'B', isDone: false }),
      EmberObject.create({ title: 'C', isDone: false }),
    ]));
  },

  incomplete: computed(
    // 'todos.@each',
    'todos.[]',
    // '[email protected]',
    function() {
      let todos = this.todos;
      return todos.filterBy('isDone', false);
    }
 	),
  
  actions: {
  	completeTodo(todo) {
    	todo.set('isDone', true);
    },
    
    addTodo() {
    	this.todos.pushObject(
      	EmberObject.create({ title: 'D', isDone: false })
      );
    }
  }
});

templates.application\.hbs

{{#each this.incomplete as |todo|}}
	<div>
  	{{todo.title}}
    
    {{#unless todo.isDone}}
    	<button onClick={{action "completeTodo" todo}}>Complete</button>
    {{/unless}}
   </div>
{{/each}}

<br>

<button onClick={{action "addTodo"}}>Add Todo</button>

twiddle\.json

{
  "version": "0.17.1",
  "EmberENV": {
    "FEATURES": {},
    "_TEMPLATE_ONLY_GLIMMER_COMPONENTS": false,
    "_APPLICATION_TEMPLATE_WRAPPER": true,
    "_JQUERY_INTEGRATION": true
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.js",
    "ember": "3.18.1",
    "ember-template-compiler": "3.18.1",
    "ember-testing": "3.18.1"
  },
  "addons": {
    "@glimmer/component": "1.0.0"
  }
}