equal

controllers.application.js

import Ember from 'ember';

function createChecklist(i) {
  return Ember.Object.create({
    key: i
  });
}

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  checklists: Ember.A(createChecklist(1), createChecklist(2), createChecklist(3)),
  currentChecklist: null,
  isLastChecklist: Ember.computed.equal('currentChecklist', 'checklists.lastObject'),
  isFirstChecklist: Ember.computed.equal('currentChecklist', 'checklists.firstObject'),
  
  actions: {
    setFirstChecklist() {
      this.set('currentChecklist', 'checklists.firstObject');
    },
    setLastChecklist() {
      this.set('currentChecklist', 'checklists.lastObject');
    }
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
<h2>isFirstChecklist: {{isFirstChecklist}}</h2>
<h2>isLastChecklist: {{isLastChecklist}}</h2>
<br>
<br>
<button {{action 'setLastChecklist'}}>
  I'm last
</button>

<button {{action 'setFirstChecklist'}}>
  I'm first
</button>

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"
  }
}