length'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 1</span>
<span aria-hidden="true" class="line-numbers-rows"><a href="#C5_L1" id=C5_L1></a><a href="#C5_L2" id=C5_L2></a><a href="#C5_L3" id=C5_L3></a><a href="#C5_L4" id=C5_L4></a><a href="#C5_L5" id=C5_L5></a></span></code></pre>
<p>If we change the todo's <code>isDone</code> property, the <code>incomplete</code> property is updated
automatically:</p>
<pre class="language-javascript