What is `return of ()` syntax : <p>I'm looking at this snippet of code:</p>

<p><a href="https://i.stack.imgur.com/JZXP5.png" rel="noreferrer"><img src="https://i.stack.imgur.com/JZXP5.png" alt="enter image description here"></a></p>

<p>It's typescript. On the first line there is:</p>

<pre><code>... return of (true);
</code></pre>

<p>What's this syntax?</p>
