как оставить ? не знаю
<script src="http://code.jquery.com/jquery-latest.min.js"></script>
<script src="http://cloud.github.com/downloads/digitalBush/jquery.maskedinput/jquery.maskedinput-1.3.min.js"></script>
<script>
jQuery(function($) {
$('select[name="cat"]').on('change', function (e) {
var inp = $("#product");
inp.val('');
var str = $(this).val() + ' ***********';
inp.mask(str,{placeholder:" _"});
inp.focus();
});
$('select[name="cat"]').change();
});
</script>
</head>
<body>
<form name="entry_form">
<select name="cat" class="text" id="Cat">
<option value="?">?</option>
<option value="PER">Persian</option>
<option value="MCO">Maine Coon</option>
</select>
<p>
<input id="product" type="text" size="35" />
</p>
</form>