if i have a select to chang input autocomplete url,what should I do?

[lcat]

var selectVal;
$('select').change(function(){
selecrVal = $(this).val();
});
$('#ac_ipt').autocomplete({
url: 'do.php',
extraParams: {search_type: selectVal},
remoteDataType: 'json',
minChars: 1
});
this not work,what should I do?