Get Value From Dropbox Snippet

In the "Client before" event of the button you can get the value of the dropdown as follows:
http://stackoverflow.com/questions/2780566/to-get-selected-value-of-a-dropdown-select-element-in-jquery

The snippet is named: vista_tabellabolle_snippet

and in the drop down list i get a result of concat mysql query, something like this:
--ID------DAY----DATE

3213123 - MON - 31/03/2012

3213124 - MON - 31/03/2012

3213125 - TUE - 31/03/2012

etc...
in the client before i've added this code but won't works:
var value = $('#vista_tabellabolle_snippet:selected').text();

alert (value);
the result is nothing in the alert box.

Simone, the selector is wrong. You have to get the id of the dropdown not the php snippet name. Check this jquery crash course: http://www.1stwebdesigner.com/tutorials/jquery-beginners-1/

But the dropdown is generated by snippet, where can i get the id name of this dropdown?

Check the following code:
global $conn;

$str = "";

$str.= "<select .value;\"><option value=\"\">Seleziona un giro</option>";

//select values from database

$strSQL = "select concat(IdConsegna,' - ',Giro,' - ',DataConsegna) as IdConsegna from vista_tabellaconsegne";

$rs = db_query($strSQL,$conn);

while ($data = db_fetch_array($rs))

$str.="<option value=>".$data["IdConsegna"]."</option>";

$str.="</select>";

echo $str;
var value = $('#[color="#FF0000"][b]my_dropdown_id:selected').text();

alert (value);

This is my working solution:
add snippet for create dropdown:

in the button (client before)