Add Clear Button to Comment Field?
OPTION 1


Use hook_form_alter to add a Clear or Cancel button/anchor tag(blank)
Add simple JS code to clear the fields


OPTION 2


Use hook_form_alter to add a Clear or Cancel button/anchor tag(blank)
Use Drupal AJAX Framework


UPDATE

You can use the hook_form_alter() inside your template.php file which is better based on your comment being more on the front-end side.

Next is you just need to get the ID of the form you want to alter/update by its form id value and just converting the dashes to underscores. An example would be:

&lt;form id="leo-form"&gt;
  // form elements here
&lt;/form&gt;


then you need to target it in your hook_form_alter() like so:

// Implements hook_form_alter.
function themename_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  if ($form_id == 'leo_form') {
    // place your code to add the clear button here
  }
}