In fact, I found It !
if($(this).hasClass('bug'))
$('#object option[value="4"]').prop("selected", true);
bug : the name of my tab object : I rename the name of my previous ID :
user.object
to :
object
because JavaScript doesn't like the dot "." in the ID name ! So
<select class="form-control" checked id="***object***" name="user.object">
<option selected value="">choisir l'objet de votre demande *</option>
#foreach($k in [1..$!localization.funnel.form.contact.object.size()])
<option value="$k">$!localization.funnel.form.contact.object.get("$k").text</option>
#end
</select>
Ale