```javascript
/**
* Makes form data persistent by storing the data in cookies.
*/
(function($){
/**
* Load value from cookie, and set cookie when value is changed.
*/
$.fn.persist = function(namespace) {
if(!namespace) {
namespace = "";
}
return this.each(function() {
var $this = $(this);
var id = $this.attr('id');
var cookie_name = namespace + id;
var value;
// Store changes in a cookie
$this.change(function() {
$.cookie(cookie_name, $this.val());
});
value = $.cookie(id);
// Don't overwrite value if it's set
if(!$this.val()) {
$this.val(namespace + value);
}
});
};
})(jQuery);
$(document).ready(function(){
$('.persistent').persist();
});
```