title: How to get selected value of a dropdown menu in ReactJS
body: <p>I'm using react and I want to get the value of the selected option of a dropdown in react but I don't know how. Any suggestions? thanks!
  My dropdown is just a select like:</p>
  
  <pre><code>&lt;select id = "dropdown"&gt;
      &lt;option value="N/A"&gt;N/A&lt;/option&gt;
      &lt;option value="1"&gt;1&lt;/option&gt;
      &lt;option value="2"&gt;2&lt;/option&gt;
      &lt;option value="3"&gt;3&lt;/option&gt;
      &lt;option value="4"&gt;4&lt;/option&gt;
  &lt;/select&gt;
  </code></pre>