That's it, dialog.prompt return a 'undefined' value.
Is correct to access form filled data use this.value? I'm testing documentation examples. Code:
<script type="text/javascript"> Meteora.uses('Meteora.Form'); Meteora.uses('Meteora.Dialog');
function novaLlicenciaPrompt() { Dialog.prompt( '{$npr_denominacio_nva_llicencia}', { 'title': '{$npr_titol_nova_llicencia}', 'onOk': function(dialog) { if (this.value != "") { Dialog.alert('Your password was: '+this.value); dialog.close(); } else { Dialog.alert('Please fill the blank'); } } } ); } </script> In the html page
<input type="button" value="{$npr_nou_tipus_llicencia}" onClick="novaLlicenciaPrompt();" />
The '{$npr_titol_nova_llicencia}' and '{$npr_denominacio_nva_llicencia}' are Smarty tags for internalization. I parse javascript templates as separate html templates.
The prompt is a option if in a <select> in the form is not present an <option> right for the user. In this case, user press a button that shows the prompt. In this prompt, user fill the desired data and this data is used in the main form.