title: How to add the "hidden" attribute to, and then remove it from an existing HTML 5 element?
body: <p>I have a button that I would like to be able to make appear and disappear on the page as needed.
  I can have the button hidden to begin with, using the hidden attribute.</p>
  <pre><code>&lt;button type=&quot;button btn-primary&quot; id=&quot;peekaboo-button&quot; hidden&gt;Peekaboo&lt;/button&gt;
  </code></pre>
  <p>I can then have the button appear by removing the hidden attribute using the removeAttribute function in the DOM.</p>
  <pre><code>document.getElementById(&quot;peekaboo-button&quot;).removeAttribute(&quot;hidden&quot;);
  </code></pre>
  <p>I need to learn how to add the hidden attribute back to the button element to hide it again.</p>