Regra css em documento java script

Como inserir um trecho no código abaixo para que o input da função pegue uma classe .error do jquery validate??

<script type="text/javascript">
;(function( $ ) {

 // Browser supports HTML5 multiple file?
 var multipleSupport = typeof $('<input/>')[0].multiple !== 'undefined',
 isIE = /msie/i.test( navigator.userAgent );

 $.fn.customFile = function() {

 return this.each(function() {

 var $file = $(this).addClass('customfile'), // the original file input
 $wrap = $('<div class="customfile-wrap">'),
 $input = $('<input type="text" class="customfile-filename" />'),
 // Button that will be used in non-IE browsers
 $button = $('<button type="button" class="customfile-upload">Selecionar</button>'),
 // Hack for IE
 $label = $('<label class="customfile-upload" for="'+ $file[0].id +'">Selecionar</label>');

 // Hide by shifting to the left so we
 // can still trigger events
 $file.css({
 position: 'absolute',
 left: '-9999px'
 });

 $wrap.insertAfter( $file )
 .append( $file, $input, ( isIE ? $label : $button ) );

 // Prevent focus
 $file.attr('tabIndex', -1);
 $button.attr('tabIndex', -1);

 $button.click(function () {
 $file.focus().click(); // Open dialog
 });

 $file.change(function() {

 var files = [], fileArr, filename;

 // If multiple is supported then extract
 // all filenames from the file array
 if ( multipleSupport ) {
 fileArr = $file[0].files;
 for ( var i = 0, len = fileArr.length; i < len; i++ ) {
 files.push( fileArr[i].name );
 }
 filename = files.join(', ');

 // If not supported then just take the value
 // and remove the path to just show the filename
 } else {
 filename = $file.val().split('\\').pop();
 }

 $input.val( filename ) // Set the value
 .attr('title', filename) // Show filename in title tootlip
 .focus(); // Regain focus

 });

 $input.on({
 blur: function() { $file.trigger('blur'); },
 keydown: function( e ) {
 if ( e.which === 13 ) { // Enter
 if ( !isIE ) { $file.trigger('click'); }
 } else if ( e.which === 8 || e.which === 46 ) { // Backspace & Del
 // On some browsers the value is read-only
 // with this trick we remove the old input and add
 // a clean clone with all the original events attached
 $file.replaceWith( $file = $file.clone( true ) );
 $file.trigger('change');
 $input.val('');
 } else if ( e.which === 9 ){ // TAB
 return;
 } else { // All other keys
 return false;
 }
 }
 });

 });

 };

 // Old browser fallback
 if ( !multipleSupport ) {
 $( document ).on('change', 'input.customfile', function() {

 var $this = $(this),
 // Create a unique ID so we
 // can attach the label to the input
 uniqId = 'customfile_'+ (new Date()).getTime(),
 $wrap = $this.parent(),

 // Filter empty input
 $inputs = $wrap.siblings().find('.customfile-filename')
 .filter(function(){ return !this.value }),

 $file = $('<input type="file" id="'+ uniqId +'" name="'+ $this.attr('name') +'"/>');

 // 1ms timeout so it runs after all other events
 // that modify the value have triggered
 setTimeout(function() {
 // Add a new input
 if ( $this.val() ) {
 // Check for empty fields to prevent
 // creating new inputs when changing files
 if ( !$inputs.length ) {
 $wrap.after( $file );
 $file.customFile();
 }
 // Remove and reorganize inputs
 } else {
 $inputs.parent().remove();
 // Move the input so it's always last on the list
 $wrap.appendTo( $wrap.parent() );
 $wrap.find('input').focus();
 }
 }, 1);

 });
 }

}( jQuery ));

$('input[type=file]').customFile();
</script>