Passing data down

application.controller.js

import Ember from 'ember';

export default Ember.Controller.extend({
  currentIndex: 0,
  
  actions: {
  	changeIndex(value, e) {
    	if (e.which === 40 || e.which === 38) {
      	this.set('currentIndex', this.get('currentIndex') - (39 - e.which));
      }
    }
  }
});

application.template.hbs

<h1>Computed testing</h1>

<p>Focus the input and use the up/down arrow keys to change the selected item.</p>

{{ input key-up="changeIndex" }}

{{ dummy-list currentIndex=currentIndex }}

dummy-item.component.js

import Ember from 'ember';

export default Ember.Component.extend({
  classNameBindings: ['isActive']
});

dummy-item.template.hbs

{{ item }}

dummy-list.component.js

import Ember from 'ember';

export default Ember.Component.extend({
  items: [
  	'one',
    'two',
    'three'
  ]
});

dummy-list.template.hbs

{{#each items as |item index|}}
	{{ dummy-item item=item isActive=(eq currentIndex index) }}
{{/each}}

helpers.eq.js

import Ember from 'ember';

export function eq([left, right]) {
    return left === right;
}

export default Ember.Helper.helper(eq);

styles.app.css

body {
  margin: 12px 16px;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 12pt;
}

.is-active {
  border-left: 5px solid #ccc;
  padding: 10px;
}

twiddle.json

{
  "version": "0.4.11",
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/1.13.9/ember.debug.js",
    "ember-data": "https://cdnjs.cloudflare.com/ajax/libs/ember-data.js/1.13.11/ember-data.js",
    "ember-template-compiler": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/1.13.9/ember-template-compiler.js"
  }
}