</code> narrows to <code>string | number</code> because
the check allows it to be either string or number.</p>
<h2 id="instanceof-narrowing"><a href="#instanceof-narrowing">Instanceof Narrowing</h2></a>
<p><code>instanceof</code> narrowing looks similar to normal narrowing, and
behaves similarly, but its rules are somewhat different. It only
applies to certain <code>instanceof</code> checks and type predicates.</p>
<p>Here's a use of <code>instanceof</code> that follows the normal narrowing rules:</p>
<p><p