New Twiddle

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  init() {
    var times = [];
    for (let i = 0; i < 10; i++) {
      times.push(Date.now() - i * 1000);
    }
    this.times = times;
  },
  
  actions: {
    add() {
      this.times.pushObject(Date.now() - this.times.length * 1000);
    },
    remove() {
      this.times.shiftObject();
    }
  }
});

helpers.my-helper.js

import Ember from 'ember';

let clock = Ember.Object.extend(Ember.Evented).create();

setInterval(() => {
  clock.trigger('tick');
}, 1000);

export default Ember.Helper.extend({
  clock,
  init() {
    this._super(...arguments);
    this.clockHandled = false;
  },
  compute(params, hash) {
    if (!this.clockHandled) {
      if (hash.autoUpdate) {
        clock.on('tick', () => Ember.run.join(() => this.recompute()));
      }
      this.clockHandled = true;
    }
    return (Date.now() - params[0]) / 1000;
  },
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{#each times as |time|}}
  {{myHelper time autoUpdate=true}}<br />
{{/each}}
<button {{action "add"}}>Add time</button><button {{action "remove"}}>Remove time</button>
<br />
Should not update: <br />
{{myHelper times.firstObject}}

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"
  }
}