e>update</code> is called in addition to <code>undo</code> and <code>redo</code>.</li>
<li><strong>comparator:</strong> A function that takes two arguments <code>a</code> and <code>b</code>
and returns <code>true</code> if they are identical and <code>false</code> if they
are not. Used to avoid pushing duplicate states to the stack.
Defaults to naive equality.</li>
</ul>             </td>             <td class="code">               <div class="highlight"><pre>  <span class="nv">constructor: </span><span cla