function checkform(form) {
    for (var x=0; form.elements[x]; x++ ) {
        if (form.elements[x].value == ""){
            if(form.elements[x].className != "nocheck") {
            alert( "U bent iets vergeten in te vullen!" );
            form.elements[x].focus();
            return false ;
            }
        }
    }       
}