n the way up.
(Hint: require users to specify <code>Nodename_downward</code> and/or <code>Nodename_upward</code> methods in their class,
then use string concatenation to construct method names while traversing the tree.)</p>
<h3 class="exercise">Aggregating across files</h3>
<p>Create a command-line program called <code>sniff.js</code>
that checks for style violations in any number of source files.
The first command-line argument to <code>sniff.js</code> must be a JavaScript source file
that exports a class