JSFiddle - React, Tailwind, and code Playground

HTML

<form action="" method="post" id="subnewtopicform" />           
  Title:
 <input type="text" name="title" /><br/>
 <input type="submit" value="Submit Topic" class="button-primary" name="subnewtopic" id="subnewtopic" /> 
</form>
  
<div id="submitted" style="display:none">Submitting...</div>

JavaScript

jQuery("#subnewtopicform").submit(function(e) {

    // Hide button by button ID
    jQuery("#subnewtopic").hide();
    
    // Show hidden div
    jQuery("#submitted").show();
});