 convert it into a native Date object via a custom mapper
        .uint32(&apos;timestamp&apos;)
        .map.callback(&apos;timestamp&apos; t =&gt; new Date(t))

        .uint32(&apos;dataCount&apos;);
});</code>
</code></pre>
<p>This is all we need for parsing any header of this structure. See how this assert makes sure we have the correct file? And how we&apos;re able to convert an uint32 into a native js Date object? This is how we roll.</p>
<h3 id="the-index-parser">The index parser</h3><p>Let&apos;s s