animation

components.my-component-will-work.js

import Ember from 'ember';

export default Ember.Component.extend({
  didRender() {
    // Force browser to draw before applying animaton.
    this.$('.box')[0].offsetHeight;
    this.$('.box').addClass('active-section');
  }
});

components.my-component.js

import Ember from 'ember';

export default Ember.Component.extend({
  didRender() { 
    Ember.run.scheduleOnce('afterRender', this, function() {
  		this.$('.box').addClass('active-section'); 
    });
  }
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle'
});

styles.app.css

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

.box {
	background-color: steelblue;
  width: 50px;
  height: 50px;
  opacity: 0;
}  

.active-section {
   opacity: 1;
   transform: translateY(0);
   transition: opacity 3s, transform 3s;
}

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{#my-component}}
	<div class="box"></div>
{{/my-component}}
<br>
<br>

{{#my-component-will-work}}
	<div class="box"></div>
{{/my-component-will-work}}

templates.components.my-component-will-work.hbs

{{yield}}

templates.components.my-component.hbs

{{yield}}

twiddle.json

{
  "version": "0.11.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.10.2",
    "ember-data": "2.11.0",
    "ember-template-compiler": "2.10.2",
    "ember-testing": "2.10.2"
  },
  "addons": {}
}