/span>
    <span class="token comment">// Because both firstName and lastName were set, this observer will fire twice.</span>
  <span class="token punctuation">}</span><span class="token punctuation">)</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

person<span class="token punctuation">.</span><span class="token function">set</span><span class="token punctuation">(</span><span class="token string">'firstName'</span><span class