se. This function can be anything
but a common practice is to call <code>console.assert</code> to dump the error to the
console.</p>
<div class="filename javascript"><div class="ribbon"></div><span>app/app.js</span><pre class="language-javascript line-numbers"><code class="javascript language-javascript">Ember<span class="token punctuation">.</span><span class="token constant">RSVP</span><span class="token punctuation">.</span><span class="token function">on</span><span class="token punctuation">(</span><sp