JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.0.0-beta1/jquery.js"></script>
<form id="main-form" method="get">
  <select name="num" required>
  <option value="1">Add Anouncment</option>
  <option value="2">Del Anouncment</option>
  <option value="3">Aprove </option>
  <option value="4">unAprove </option>
  </select> 
  <input name="Anouncement" type="text" required> 
  <input name="Submit"  type="button" value="Update" id="submit_btn"/>
</form>

JavaScript

$('#submit_btn').on('click', function(e) {
	e.preventDefault();
  console.log($('[name="num"]').val());
});