JSFiddle - React, Tailwind, and code Playground

HTML

<div id='preview'></div>
<form id='yourForm' action="submit.php" method="post">
    Enter Title:<input type="text" name="title" size="20"><BR>
    Enter Class Code:<input type="text" name="class" size="20"><BR>
    Enter Base Number:<input type="text" name="base" size="20"><BR>
    Enter Dash Number:<input type="text" name="dash" size="20"><BR>
    <input type="submit" value="Submit">
</form>

JavaScript

$('#yourForm input').keyup(function(e) {
    var docNum = 'Your Document Number: <br/>' + $('input[name="class"]').val() + '-' + $('input[name="base"]').val() + '-' + $('input[name="dash"]').val();
    $('#preview').html(docNum);
});