JSFiddle - React, Tailwind, and code Playground

HTML

<form method="post" id="form" action="admin/insertShoutBox" >
        <input type="hidden" name="user_id" id="user_id" value="1" />
        <input type="hidden" name="user" id="nick" value="admin" />
        <p class="messagelabel"><label class="messagelabel">Message</label>
            <textarea  id="message" name="message" rows="2" cols="80"></textarea>
        </p>
        <div class="buttons">
            <button type="submit" class="positive" name="submit" value="submit">
            <img src="http://localhost/kaimonokago3/assets/icons/disk.png" alt="disk"/>            Save            </button>
        </div>
    </form>

JavaScript

$(document).ready(function(){
    //global vars
    var inputUser = $("#nick");
    var inputMessage = $("#message");

    //check if all fields are filled
    function checkForm()
    {
        if(inputUser.val() && inputMessage.val())
        {
            return true;
        }   
        else
        {
            return false;
        }      
    }
    
    
    //on submit event
    $("#form").submit(function(event){
        event.preventDefault();
        if(checkForm())
        {
            
        }
        else alert("Please fill all fields!");
        //we prevent the refresh of the page after submitting the form
        return false;
    });
});