I want to know how to only activate the form submit, not getting value to ajax url in jquery?

I want to submit a form without refresh page. My case is different than most people, I only need to initial the form submit, and then in the php, if $_POST, then gather the value. It is not duplicate question, because most answers are sending the form value to .ajax url and send the value back to html. I just want to initialize the submit.

$.ajax({
    url:'member_search.php',
    type:'POST',
        data:{
      search_text: $(".result_tag").text()
        }
    
  });

<form action="" method="post" name="form">
  <input type="hidden" id="word" value="hello" name="input" >
  </form>

<?php
if ($_POST){
  $value=$_POST['input'];
   echo $value;



?>