title: How do I tell if a prop was passed in a react component
body: <p>I have a react function component, This function takes in some props.</p>
  <p>I want to know if the component had a specific prop passed to it.</p>
  <p>Say I have a component, Song, that takes in 1 prop, Genre. I would want to know if the component when used was used with the genre prop.</p>
  <p>examples:</p>
  <ul>
  <li>genre not passed:</li>
  </ul>
  <pre class="lang-js prettyprint-override"><code>&lt;Song&gt;&lt;/Song&gt;
  </code></pre>
  <ul>
  <li>genre passed:</li>
  </ul>
  <pre class="lang-js prettyprint-override"><code>&lt;Song genre=&quot;Rap&quot;&gt;&lt;/Song&gt;
  </code></pre>
  <p>edit: clarity</p>