[Weise]

сейчас такой вариант:

// JavaScript Document
function doLoad(value){
    
    var req = new JsHttpRequest();
	
    value=encodeURIComponent(value);
    var query="name="+value;
    // Prepare request object (automatically choose GET or POST).
    req.open(null, '../chat/add_mess.php', true);
    // Send data to backend.
    req.send( { q: query } );
	
}

<form method='POST' action='#' id='add_message' enctype='multipart/form-data' onSubmit='return false'>
        <input id='message' name='message' type='text' maxsize='250' size='50'>

        <input type='button' class='submit' onClick='doLoad(document.getElementById(add_message))' value='Отправить'>
    </form>