JSFiddle - React, Tailwind, and code Playground

HTML

<form  method="POST" name="form" action="index2.php">
    <table>
            <!--for each PHP-->
        <tr>
            <td><input type='checkbox' name='dirid[]' value='phpResult'/></td>
            <!--other fields-->
        </tr>
            <!-- END for each PHP-->
    </table>
        <input type="submit" name="add" value="Add" />
        <input type="submit" name="edit" value="Edit" />
        <input type="submit" name="delete" value="Delete" />
</form>

JavaScript

$(document).ready(function(){
    
 $("form").submit(function() {
    var a = false;//here the condition you want if true will submit
    if (a) {
        alert("YES");
        return true;
    }else{
        alert("NO");
        return false;
    }
    });
    
});