improved version of Combobox code from jQuery UI docs

jquery.combobox.js

/**
   Copyright 2011 Couchbase, Inc.

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
**/
/**
 * @author Benjamin Young <byoung@bigbluehat.com>
 *
 * Original code came from:
 * @link http://jqueryui.com/demos/autocomplete/#combobox
 **/
;(function($){
  /**
   * Combobox widget
   * @link http://jqueryui.com/demos/autocomplete/#combobox
   */
  $.widget( "ui.combobox", {
    _create: function() {
      var self = this,
          select = this.element.hide(),
          selected = select.children( ":selected" ),
          value = selected.val() ? selected.text() : "";
      var input = this.input = $( "<input>" )
        .insertAfter( select )
        .val( value )
        .autocomplete({
          delay: 0,
          minLength: 0,
          source: function( request, response ) {
            var matcher = new RegExp( $.ui.autocomplete.escapeRegex(request.term), "i" );
            response( select.children( "option" ).map(function() {
              var text = $( this ).text();
              if ( this.value && ( !request.term || matcher.test(text) ) )
                return {
                  label: text.replace(
                    new RegExp(
                      "(?![^&;]+;)(?!<[^<>]*)(" +
                      $.ui.autocomplete.escapeRegex(request.term) +
                      ")(?![^<>]*>)(?![^&;]+;)", "gi"
                    ), "<strong>$1</strong>" ),
                  value: text,
                  option: this
                };
            }) );
          },
          select: function( event, ui ) {
            ui.item.option.selected = true;
            self._trigger( "selected", event, {
              item: ui.item.option
            });
            select.trigger('change');
          },
          change: function( event, ui ) {
            if ( !ui.item ) {
              var matcher = new RegExp( "^" + $.ui.autocomplete.escapeRegex( $(this).val() ) + "$", "i" ),
                  valid = false;
              select.children( "option" ).each(function() {
                if ( $( this ).text().match( matcher ) ) {
                  this.selected = valid = true;
                  return false;
                }
              });
              if ( !valid ) {
                // remove invalid value, as it didn't match anything
                $( this ).val( "" );
                select.val( "" );
                input.data( "autocomplete" ).term = "";
                $(this).trigger('focus');
                self.button.trigger('click');
                return false;
              }
            }
          }
        })
        .addClass( "ui-widget ui-widget-content ui-corner-left" );

      input.click(function() {
          $(this).select();
        })
        .keydown(function(ev) {
          var visible = $(this).autocomplete('widget').find('li:visible');
          // catch tab and enter keys
          if (ev.which == 9 || ev.which == 13) {
            if (visible.length == 1) {
              $(this).val($(visible[0]).text())
                .prev('select').find('option:contains('+$(visible[0]).text()+')')
                .attr('selected', 'selected').trigger('change');
            } else if (visible.length > 1) {
              ev.preventDefault();
            }
            if (ev.which == 13) {
              $(this).blur();
            }
          }
        })
        .data( "autocomplete" )._renderItem = function( ul, item ) {
          return $( "<li></li>" )
            .data( "item.autocomplete", item )
            .append( "<a>" + item.label + "</a>" )
            .appendTo( ul );
        };

      this.button = $( "<button type='button'>&nbsp;</button>" )
        .attr( "tabIndex", -1 )
        .attr( "title", "Show All Items" )
        .insertAfter( input )
        .button({
          icons: {
            primary: "ui-icon-triangle-1-s"
          },
          text: false
        })
        .removeClass( "ui-corner-all" )
        .addClass( "ui-corner-right ui-button-icon" )
        .click(function() {
          // close if already visible
          if ( input.autocomplete( "widget" ).is( ":visible" ) ) {
            input.autocomplete( "close" );
            return;
          }

          // pass empty string as value to search for, displaying all results
          input.autocomplete( "search", "" );
          input.focus();
        });
    },

    destroy: function() {
      this.input.remove();
      this.button.remove();
      this.element.show();
      $.Widget.prototype.destroy.call( this );
    }
  });
})(jQuery);