h a simple example.
We have a <code>Person</code> object with <code>firstName</code> and <code>lastName</code> properties, but we also want a <code>fullName</code> property that joins the two names when either of them changes:</p>
<pre class="language-javascript line-numbers"><code class="javascript language-javascript">Person <span class="token operator">=</span> Ember<span class="token punctuation">.</span>Object<span class="token punctuation">.</span><span class="token function">extend</span><span class=