jQuery UI Autocomplete Combobox Very Slow With Large Select Lists

With the current combobox implementation, the full list is emptied and re-rendered every time you expand the dropdown. Also you are stuck with setting the minLength to 0, because it has to do an empty search to get the full list.

Here is my own implementation extending the autocomplete widget. In my tests it can handle lists of 5000 items pretty smoothly even on IE 7 and 8. It renders the full list just once, and reuses it whenever the dropdown button is clicked. This also removes the dependence of the option minLength = 0. It also works with arrays, and ajax as list source. Also if you have multiple large list, the widget initialization is added to a queue so it can run in the background, and not freeze the browser.

<script>(function($){    $.widget( "ui.combobox", $.ui.autocomplete,         {        options: {             /* override default values here */            minLength: 2,            /* the argument to pass to ajax to get the complete list */            ajaxGetAll: {get: "all"}        },        _create: function(){            if (this.element.is("SELECT")){                this._selectInit();                return;            }            $.ui.autocomplete.prototype._create.call(this);            var input = this.element;            input.addClass( "ui-widget ui-widget-content ui-corner-left" );            this.button = $( "<button type='button'> </button>" )            .attr( "tabIndex", -1 )            .attr( "title", "Show All Items" )            .insertAfter( input )            .button({                icons: { primary: "ui-icon-triangle-1-s" },                text: false            })            .removeClass( "ui-corner-all" )            .addClass( "ui-corner-right ui-button-icon" )            .click(function(event) {                // close if already visible                if ( input.combobox( "widget" ).is( ":visible" ) ) {                    input.combobox( "close" );                    return;                }                // when user clicks the show all button, we display the cached full menu                var data = input.data("combobox");                clearTimeout( data.closing );                if (!input.isFullMenu){                    data._swapMenu();                    input.isFullMenu = true;                }                /* input/select that are initially hidden (display=none, i.e. second level menus),                    will not have position cordinates until they are visible. */                input.combobox( "widget" ).css( "display", "block" )                .position($.extend({ of: input },                    data.options.position                    ));                input.focus();                data._trigger( "open" );            });            /* to better handle large lists, put in a queue and process sequentially */            $(document).queue(function(){                var data = input.data("combobox");                if ($.isArray(data.options.source)){                     $.ui.combobox.prototype._renderFullMenu.call(data, data.options.source);                }else if (typeof data.options.source === "string") {                    $.getJSON(data.options.source, data.options.ajaxGetAll , function(source){                        $.ui.combobox.prototype._renderFullMenu.call(data, source);                    });                }else {                    $.ui.combobox.prototype._renderFullMenu.call(data, data.source());                }            });        },        /* initialize the full list of items, this menu will be reused whenever the user clicks the show all button */        _renderFullMenu: function(source){            var self = this,                input = this.element,                ul = input.data( "combobox" ).menu.element,                lis = [];            source = this._normalize(source);             input.data( "combobox" ).menuAll = input.data( "combobox" ).menu.element.clone(true).appendTo("body");            for(var i=0; i<source.length; i++){                lis[i] = "<li class=\"ui-menu-item\" role=\"menuitem\"><a class=\"ui-corner-all\" tabindex=\"-1\">"+source[i].label+"</a></li>";            }            ul.append(lis.join(""));            this._resizeMenu();            // setup the rest of the data, and event stuff            setTimeout(function(){                self._setupMenuItem.call(self, ul.children("li"), source );            }, 0);            input.isFullMenu = true;        },        /* incrementally setup the menu items, so the browser can remains responsive when processing thousands of items */        _setupMenuItem: function( items, source ){            var self = this,                itemsChunk = items.splice(0, 500),                sourceChunk = source.splice(0, 500);            for(var i=0; i<itemsChunk.length; i++){                $(itemsChunk[i])                .data( "item.autocomplete", sourceChunk[i])                .mouseenter(function( event ) {                    self.menu.activate( event, $(this));                })                .mouseleave(function() {                    self.menu.deactivate();                });            }            if (items.length > 0){                setTimeout(function(){                    self._setupMenuItem.call(self, items, source );                }, 0);            }else { // renderFullMenu for the next combobox.                $(document).dequeue();            }        },        /* overwrite. make the matching string bold */        _renderItem: function( ul, item ) {            var label = item.label.replace( new RegExp(                "(?![^&;]+;)(?!<[^<>]*)(" + $.ui.autocomplete.escapeRegex(this.term) +                 ")(?![^<>]*>)(?![^&;]+;)", "gi"), "<strong>$1</strong>" );            return $( "<li></li>" )                .data( "item.autocomplete", item )                .append( "<a>" + label + "</a>" )                .appendTo( ul );        },        /* overwrite. to cleanup additional stuff that was added */        destroy: function() {            if (this.element.is("SELECT")){                this.input.remove();                this.element.removeData().show();                return;            }            // super()            $.ui.autocomplete.prototype.destroy.call(this);            // clean up new stuff            this.element.removeClass( "ui-widget ui-widget-content ui-corner-left" );            this.button.remove();        },        /* overwrite. to swap out and preserve the full menu */         search: function( value, event){            var input = this.element;            if (input.isFullMenu){                this._swapMenu();                input.isFullMenu = false;            }            // super()            $.ui.autocomplete.prototype.search.call(this, value, event);        },        _change: function( event ){            abc = this;            if ( !this.selectedItem ) {                var matcher = new RegExp( "^" + $.ui.autocomplete.escapeRegex( this.element.val() ) + "$", "i" ),                    match = $.grep( this.options.source, function(value) {                        return matcher.test( value.label );                    });                if (match.length){                    match[0].option.selected = true;                }else {                    // remove invalid value, as it didn't match anything                    this.element.val( "" );                    if (this.options.selectElement) {                        this.options.selectElement.val( "" );                    }                }            }                            // super()            $.ui.autocomplete.prototype._change.call(this, event);        },        _swapMenu: function(){            var input = this.element,                 data = input.data("combobox"),                tmp = data.menuAll;            data.menuAll = data.menu.element.hide();            data.menu.element = tmp;        },        /* build the source array from the options of the select element */        _selectInit: function(){            var select = this.element.hide(),            selected = select.children( ":selected" ),            value = selected.val() ? selected.text() : "";            this.options.source = select.children( "option[value!='']" ).map(function() {                return { label: $.trim(this.text), option: this };            }).toArray();            var userSelectCallback = this.options.select;            var userSelectedCallback = this.options.selected;            this.options.select = function(event, ui){                ui.item.option.selected = true;                if (userSelectCallback) userSelectCallback(event, ui);                // compatibility with jQuery UI's combobox.                if (userSelectedCallback) userSelectedCallback(event, ui);            };            this.options.selectElement = select;            this.input = $( "<input>" ).insertAfter( select )                .val( value ).combobox(this.options);        }    });})(jQuery);</script>

I've modified the way the results are returned (in the source function) because the map() function seemed slow to me. It runs faster for large select lists (and smaller too), but lists with several thousands of options are still very slow.I've profiled (with firebug's profile function) the original and my modified code, and the execution time goes like this:

Original: Profiling (372.578 ms, 42307 calls)

Modified: Profiling (0.082 ms, 3 calls)

Here is the modified code of the source function, you can see the original code at the jquery ui demo http://jqueryui.com/demos/autocomplete/#combobox. There can certainly be more optimization.

source: function( request, response ) {    var matcher = new RegExp( $.ui.autocomplete.escapeRegex(request.term), "i" );    var select_el = this.element.get(0); // get dom element    var rep = new Array(); // response array    // simple loop for the options    for (var i = 0; i < select_el.length; i++) {        var text = select_el.options[i].text;        if ( select_el.options[i].value && ( !request.term || matcher.test(text) ) )            // add element to result array            rep.push({                label: text, // no more bold                value: text,                option: select_el.options[i]            });    }    // send response    response( rep );},

Hope this helps.

I like the answer from Berro. But because it was still a bit slow (I had about 3000 options in select), i modified it slightly so that only first N matching results are displayed.I also added an item at the end notifying the user that more results are available and canceled focus and select events for that item.

Here is modified code for source and select functions and added one for focus:

source: function( request, response ) {    var matcher = new RegExp( $.ui.autocomplete.escapeRegex(request.term), "i" );    var select_el = select.get(0); // get dom element    var rep = new Array(); // response array    var maxRepSize = 10; // maximum response size      // simple loop for the options    for (var i = 0; i < select_el.length; i++) {        var text = select_el.options[i].text;        if ( select_el.options[i].value && ( !request.term || matcher.test(text) ) )            // add element to result array            rep.push({                label: text, // no more bold                value: text,                option: select_el.options[i]            });        if ( rep.length > maxRepSize ) {            rep.push({                label: "... more available",                value: "maxRepSizeReached",                option: ""            });            break;        }     }     // send response     response( rep );},          select: function( event, ui ) {    if ( ui.item.value == "maxRepSizeReached") {        return false;    } else {        ui.item.option.selected = true;        self._trigger( "selected", event, {            item: ui.item.option        });    }},focus: function( event, ui ) {    if ( ui.item.value == "maxRepSizeReached") {        return false;    }},