title: How to validate html textbox not to allow special characters and space?
body: <p>This is my html:</p>
  
  <pre><code> &lt;input type="text" name="folderName"&gt;
  </code></pre>
  
  <p>Here, I want to validate the textbox value by not allowing to key in special characters and space. But it should allow underscore. </p>
  
  <p>How to validate this textbox?</p>