[jQuery] How to mask and unmask

[jQuery] How to mask and unmask


I'm using the mask plugin http://digitalbush.com/projects/masked-input-plugin/.
In <head> :
<script type="text/javascript">
jQuery(function($){
$("#MYINPUT").mask("99/99/9999", {placeholder:" "});
});
</script>
this function control a combo box.
$(document).ready(function() {
$('#COMBO').change(function() {
jQuery(function($){
$("#MYINPUT").unmask().mask("999.999.999-99",
{placeholder:" "});
});
});
});
but is not working. anyone knows why?