New Twiddle

components.for-of.js

import Ember from 'ember';

const ForOf = Ember.Component.extend({
  tagName: '',
  items: Ember.computed(function() {
  	return [...this.get('_items')];
  })
});

ForOf.reopenClass({
	positionalParams: ['_items']
});

export default ForOf;

controllers.application.js

import Ember from 'ember';

class UserCollection {
  constructor(users) {
    this.users = [].concat(users);
  }

  [Symbol.iterator]() {
    let i = 0;
    let users = this.users;

    return {
      next() {
        if (i < users.length) {
          return { done: false, value: users[i++] };
        }

        return { done: true };
      }
    };
  }
}

export default Ember.Controller.extend({
  users: [
    { first: 'Yehuda', last: 'Katz' },
    { first: 'Tom', last: 'Dale' },
    { first: 'Taylor', last: 'Otwell' }
  ],
  users2: new UserCollection([
    { first: 'Yehuda', last: 'Katz' },
    { first: 'Tom', last: 'Dale' },
    { first: 'Taylor', last: 'Otwell' }
  ])
});

templates.application.hbs

<h2>Users</h2>
{{#each users2 as |user i|}}
	<p>{{i}} - {{user.first}}</p>
{{/each}}

<hr>

{{#for-of users2 as |user i|}}
	<p>{{i}} - {{user.first}}</p>
{{/for-of}}

templates.components.for-of.hbs

{{#each items as |item index|}}
	{{yield item index}}
{{/each}}

twiddle.json

{
  "version": "0.12.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.12.0",
    "ember-template-compiler": "2.12.0",
    "ember-testing": "2.12.0"
  },
  "addons": {
    "ember-data": "2.12.1"
  }
}