The source code

    /**
     * @class Ext.PagingToolbar
     * @extends Ext.Toolbar
     * <p>As the amount of records increases, the time required for the browser to render
     * them increases. Paging is used to reduce the amount of data exchanged with the client.
     * Note: if there are more records/rows than can be viewed in the available screen area, vertical
     * scrollbars will be added.</p>
     * <p>Paging is typically handled on the server side (see exception below). The client sends
     * parameters to the server side, which the server needs to interpret and then respond with the
     * approprate data.</p>
     * <p><b>Ext.PagingToolbar</b> is a specialized toolbar that is bound to a {@link Ext.data.Store}
     * and provides automatic paging control. This Component {@link Ext.data.Store#load load}s blocks
     * of data into the <tt>{@link #store}</tt> by passing {@link Ext.data.Store#paramNames paramNames} used for
     * paging criteria.</p>
     * <p>PagingToolbar is typically used as one of the Grid's toolbars:</p>
     * <pre><code>
    Ext.QuickTips.init(); // to display button quicktips

    var myStore = new Ext.data.Store({
        reader: new Ext.data.JsonReader({
            {@link Ext.data.JsonReader#totalProperty totalProperty}: 'results',
            ...
        }),
        ...
    });

    var myPageSize = 25;  // server script should only send back 25 items at a time

    var grid = new Ext.grid.GridPanel({
        ...
        store: myStore,
        bbar: new Ext.PagingToolbar({
            {@link #store}: myStore,       // grid and PagingToolbar using same store
            {@link #displayInfo}: true,
            {@link #pageSize}: myPageSize,
            {@link #prependButtons}: true,
            items: [
                'text 1'
            ]
        })
    });
     * </code></pre>
     *
     * <p>To use paging, pass the paging requirements to the server when the store is first loaded.</p>
     * <pre><code>
    store.load({
        params: {
            // specify params for the first page load if using paging
            start: 0,
            limit: myPageSize,
            // other params
            foo:   'bar'
        }
    });
     * </code></pre>
     *
     * <p>If using {@link Ext.data.Store#autoLoad store's autoLoad} configuration:</p>
     * <pre><code>
    var myStore = new Ext.data.Store({
        {@link Ext.data.Store#autoLoad autoLoad}: {params:{start: 0, limit: 25}},
        ...
    });
     * </code></pre>
     *
     * <p>The packet sent back from the server would have this form:</p>
     * <pre><code>
    {
        "success": true,
        "results": 2000,
        "rows": [ // <b>*Note:</b> this must be an Array
            { "id":  1, "name": "Bill", "occupation": "Gardener" },
            { "id":  2, "name":  "Ben", "occupation": "Horticulturalist" },
            ...
            { "id": 25, "name":  "Sue", "occupation": "Botanist" }
        ]
    }
     * </code></pre>
     * <p><u>Paging with Local Data</u></p>
     * <p>Paging can also be accomplished with local data using extensions:</p>
     * <div class="mdetail-params"><ul>
     * <li><a href="http://extjs.com/forum/showthread.php?t=71532">Ext.ux.data.PagingStore</a></li>
     * <li>Paging Memory Proxy (examples/ux/PagingMemoryProxy.js)</li>
     * </ul></div>
     * @constructor Create a new PagingToolbar
     * @param {Object} config The config object
     * @xtype paging
     */
    (function() {

    var T = Ext.Toolbar;

    Ext.PagingToolbar = Ext.extend(Ext.Toolbar, {
        /**
         * @cfg {Ext.data.Store} store
         * The {@link Ext.data.Store} the paging toolbar should use as its data source (required).
         */
        /**
         * @cfg {Boolean} displayInfo
         * <tt>true</tt> to display the displayMsg (defaults to <tt>false</tt>)
         */
        /**
         * @cfg {Number} pageSize
         * The number of records to display per page (defaults to <tt>20</tt>)
         */
        pageSize : 20,
        /**
         * @cfg {Boolean} prependButtons
         * <tt>true</tt> to insert any configured <tt>items</tt> <i>before</i> the paging buttons.
         * Defaults to <tt>false</tt>.
         */
        /**
         * @cfg {String} displayMsg
         * The paging status message to display (defaults to <tt>'Displaying {0} - {1} of {2}'</tt>).
         * Note that this string is formatted using the braced numbers <tt>{0}-{2}</tt> as tokens
         * that are replaced by the values for start, end and total respectively. These tokens should
         * be preserved when overriding this string if showing those values is desired.
         */
        displayMsg : 'Displaying {0} - {1} of {2}',
        /**
         * @cfg {String} emptyMsg
         * The message to display when no records are found (defaults to 'No data to display')
         */
        emptyMsg : 'No data to display',
        /**
         * @cfg {String} beforePageText
         * The text displayed before the input item (defaults to <tt>'Page'</tt>).
         */
        beforePageText : 'Page',
        /**
         * @cfg {String} afterPageText
         * Customizable piece of the default paging text (defaults to <tt>'of {0}'</tt>). Note that
         * this string is formatted using <tt>{0}</tt> as a token that is replaced by the number of
         * total pages. This token should be preserved when overriding this string if showing the
         * total page count is desired.
         */
        afterPageText : 'of {0}',
        /**
         * @cfg {String} firstText
         * The quicktip text displayed for the first page button (defaults to <tt>'First Page'</tt>).
         * <b>Note</b>: quick tips must be initialized for the quicktip to show.
         */
        firstText : 'First Page',
        /**
         * @cfg {String} prevText
         * The quicktip text displayed for the previous page button (defaults to <tt>'Previous Page'</tt>).
         * <b>Note</b>: quick tips must be initialized for the quicktip to show.
         */
        prevText : 'Previous Page',
        /**
         * @cfg {String} nextText
         * The quicktip text displayed for the next page button (defaults to <tt>'Next Page'</tt>).
         * <b>Note</b>: quick tips must be initialized for the quicktip to show.
         */
        nextText : 'Next Page',
        /**
         * @cfg {String} lastText
         * The quicktip text displayed for the last page button (defaults to <tt>'Last Page'</tt>).
         * <b>Note</b>: quick tips must be initialized for the quicktip to show.
         */
        lastText : 'Last Page',
        /**
         * @cfg {String} refreshText
         * The quicktip text displayed for the Refresh button (defaults to <tt>'Refresh'</tt>).
         * <b>Note</b>: quick tips must be initialized for the quicktip to show.
         */
        refreshText : 'Refresh',

        /**
         * <p><b>Deprecated</b>. <code>paramNames</code> should be set in the <b>data store</b>
         * (see {@link Ext.data.Store#paramNames}).</p>
         * <br><p>Object mapping of parameter names used for load calls, initially set to:</p>
         * <pre>{start: 'start', limit: 'limit'}</pre>
         * @type Object
         * @property paramNames
         * @deprecated
         */

        /**
         * The number of records to display per page.  See also <tt>{@link #cursor}</tt>.
         * @type Number
         * @property pageSize
         */

        /**
         * Indicator for the record position.  This property might be used to get the active page
         * number for example:<pre><code>
         * // t is reference to the paging toolbar instance
         * var activePage = Math.ceil((t.cursor + t.pageSize) / t.pageSize);
         * </code></pre>
         * @type Number
         * @property cursor
         */

        initComponent : function(){
            var pagingItems = [this.first = new T.Button({
                tooltip: this.firstText,
                overflowText: this.firstText,
                iconCls: 'x-tbar-page-first',
                disabled: true,
                handler: this.moveFirst,
                scope: this
            }), this.prev = new T.Button({
                tooltip: this.prevText,
                overflowText: this.prevText,
                iconCls: 'x-tbar-page-prev',
                disabled: true,
                handler: this.movePrevious,
                scope: this
            }), '-', this.beforePageText,
            this.inputItem = new Ext.form.NumberField({
                cls: 'x-tbar-page-number',
                allowDecimals: false,
                allowNegative: false,
                enableKeyEvents: true,
                selectOnFocus: true,
                submitValue: false,
                listeners: {
                    scope: this,
                    keydown: this.onPagingKeyDown,
                    blur: this.onPagingBlur
                }
            }), this.afterTextItem = new T.TextItem({
                text: String.format(this.afterPageText, 1)
            }), '-', this.next = new T.Button({
                tooltip: this.nextText,
                overflowText: this.nextText,
                iconCls: 'x-tbar-page-next',
                disabled: true,
                handler: this.moveNext,
                scope: this
            }), this.last = new T.Button({
                tooltip: this.lastText,
                overflowText: this.lastText,
                iconCls: 'x-tbar-page-last',
                disabled: true,
                handler: this.moveLast,
                scope: this
            }), '-', this.refresh = new T.Button({
                tooltip: this.refreshText,
                overflowText: this.refreshText,
                iconCls: 'x-tbar-loading',
                handler: this.doRefresh,
                scope: this
            })];

            var userItems = this.items || this.buttons || [];
            if (this.prependButtons) {
                this.items = userItems.concat(pagingItems);
            }else{
                this.items = pagingItems.concat(userItems);
            }
            delete this.buttons;
            if(this.displayInfo){
                this.items.push('->');
                this.items.push(this.displayItem = new T.TextItem({}));
            }
            Ext.PagingToolbar.superclass.initComponent.call(this);
            this.addEvents(
                /**
                 * @event change
                 * Fires after the active page has been changed.
                 * @param {Ext.PagingToolbar} this
                 * @param {Object} pageData An object that has these properties:<ul>
                 * <li><code>total</code> : Number <div class="sub-desc">The total number of records in the dataset as
                 * returned by the server</div></li>
                 * <li><code>activePage</code> : Number <div class="sub-desc">The current page number</div></li>
                 * <li><code>pages</code> : Number <div class="sub-desc">The total number of pages (calculated from
                 * the total number of records in the dataset as returned by the server and the current {@link #pageSize})</div></li>
                 * </ul>
                 */
                'change',
                /**
                 * @event beforechange
                 * Fires just before the active page is changed.
                 * Return false to prevent the active page from being changed.
                 * @param {Ext.PagingToolbar} this
                 * @param {Object} params An object hash of the parameters which the PagingToolbar will send when
                 * loading the required page. This will contain:<ul>
                 * <li><code>start</code> : Number <div class="sub-desc">The starting row number for the next page of records to
                 * be retrieved from the server</div></li>
                 * <li><code>limit</code> : Number <div class="sub-desc">The number of records to be retrieved from the server</div></li>
                 * </ul>
                 * <p>(note: the names of the <b>start</b> and <b>limit</b> properties are determined
                 * by the store's {@link Ext.data.Store#paramNames paramNames} property.)</p>
                 * <p>Parameters may be added as required in the event handler.</p>
                 */
                'beforechange'
            );
            this.on('afterlayout', this.onFirstLayout, this, {single: true});
            this.cursor = 0;
            this.bindStore(this.store, true);
        },

        // private
        onFirstLayout : function(){
            if(this.dsLoaded){
                this.onLoad.apply(this, this.dsLoaded);
            }
        },

        // private
        updateInfo : function(){
            if(this.displayItem){
                var count = this.store.getCount();
                var msg = count == 0 ?
                    this.emptyMsg :
                    String.format(
                        this.displayMsg,
                        this.cursor+1, this.cursor+count, this.store.getTotalCount()
                    );
                this.displayItem.setText(msg);
            }
        },

        // private
        onLoad : function(store, r, o){
            if(!this.rendered){
                this.dsLoaded = [store, r, o];
                return;
            }
            var p = this.getParams();
            this.cursor = (o.params && o.params[p.start]) ? o.params[p.start] : 0;
            var d = this.getPageData(), ap = d.activePage, ps = d.pages;

            this.afterTextItem.setText(String.format(this.afterPageText, d.pages));
            this.inputItem.setValue(ap);
            this.first.setDisabled(ap == 1);
            this.prev.setDisabled(ap == 1);
            this.next.setDisabled(ap == ps);
            this.last.setDisabled(ap == ps);
            this.refresh.enable();
            this.updateInfo();
            this.fireEvent('change', this, d);
        },

        // private
        getPageData : function(){
            var total = this.store.getTotalCount();
            return {
                total : total,
                activePage : Math.ceil((this.cursor+this.pageSize)/this.pageSize),
                pages :  total < this.pageSize ? 1 : Math.ceil(total/this.pageSize)
            };
        },

        /**
         * Change the active page
         * @param {Integer} page The page to display
         */
        changePage : function(page){
            this.doLoad(((page-1) * this.pageSize).constrain(0, this.store.getTotalCount()));
        },

        // private
        onLoadError : function(){
            if(!this.rendered){
                return;
            }
            this.refresh.enable();
        },

        // private
        readPage : function(d){
            var v = this.inputItem.getValue(), pageNum;
            if (!v || isNaN(pageNum = parseInt(v, 10))) {
                this.inputItem.setValue(d.activePage);
                return false;
            }
            return pageNum;
        },

        onPagingFocus : function(){
            this.inputItem.select();
        },

        //private
        onPagingBlur : function(e){
            this.inputItem.setValue(this.getPageData().activePage);
        },

        // private
        onPagingKeyDown : function(field, e){
            var k = e.getKey(), d = this.getPageData(), pageNum;
            if (k == e.RETURN) {
                e.stopEvent();
                pageNum = this.readPage(d);
                if(pageNum !== false){
                    pageNum = Math.min(Math.max(1, pageNum), d.pages) - 1;
                    this.doLoad(pageNum * this.pageSize);
                }
            }else if (k == e.HOME || k == e.END){
                e.stopEvent();
                pageNum = k == e.HOME ? 1 : d.pages;
                field.setValue(pageNum);
            }else if (k == e.UP || k == e.PAGEUP || k == e.DOWN || k == e.PAGEDOWN){
                e.stopEvent();
                if((pageNum = this.readPage(d))){
                    var increment = e.shiftKey ? 10 : 1;
                    if(k == e.DOWN || k == e.PAGEDOWN){
                        increment *= -1;
                    }
                    pageNum += increment;
                    if(pageNum >= 1 & pageNum <= d.pages){
                        field.setValue(pageNum);
                    }
                }
            }
        },

        // private
        getParams : function(){
            //retain backwards compat, allow params on the toolbar itself, if they exist.
            return this.paramNames || this.store.paramNames;
        },

        // private
        beforeLoad : function(){
            if(this.rendered && this.refresh){
                this.refresh.disable();
            }
        },

        // private
        doLoad : function(start){
            var o = {}, pn = this.getParams();
            o[pn.start] = start;
            o[pn.limit] = this.pageSize;
            if(this.fireEvent('beforechange', this, o) !== false){
                this.store.load({params:o});
            }
        },

        /**
         * Move to the first page, has the same effect as clicking the 'first' button.
         */
        moveFirst : function(){
            this.doLoad(0);
        },

        /**
         * Move to the previous page, has the same effect as clicking the 'previous' button.
         */
        movePrevious : function(){
            this.doLoad(Math.max(0, this.cursor-this.pageSize));
        },

        /**
         * Move to the next page, has the same effect as clicking the 'next' button.
         */
        moveNext : function(){
            this.doLoad(this.cursor+this.pageSize);
        },

        /**
         * Move to the last page, has the same effect as clicking the 'last' button.
         */
        moveLast : function(){
            var total = this.store.getTotalCount(),
                extra = total % this.pageSize;

            this.doLoad(extra ? (total - extra) : total - this.pageSize);
        },

        /**
         * Refresh the current page, has the same effect as clicking the 'refresh' button.
         */
        doRefresh : function(){
            this.doLoad(this.cursor);
        },

        /**
         * Binds the paging toolbar to the specified {@link Ext.data.Store}
         * @param {Store} store The store to bind to this toolbar
         * @param {Boolean} initial (Optional) true to not remove listeners
         */
        bindStore : function(store, initial){
            var doLoad;
            if(!initial && this.store){
                if(store !== this.store && this.store.autoDestroy){
                    this.store.destroy();
                }else{
                    this.store.un('beforeload', this.beforeLoad, this);
                    this.store.un('load', this.onLoad, this);
                    this.store.un('exception', this.onLoadError, this);
                }
                if(!store){
                    this.store = null;
                }
            }
            if(store){
                store = Ext.StoreMgr.lookup(store);
                store.on({
                    scope: this,
                    beforeload: this.beforeLoad,
                    load: this.onLoad,
                    exception: this.onLoadError
                });
                doLoad = true;
            }
            this.store = store;
            if(doLoad){
                this.onLoad(store, null, {});
            }
        },

        /**
         * Unbinds the paging toolbar from the specified {@link Ext.data.Store} <b>(deprecated)</b>
         * @param {Ext.data.Store} store The data store to unbind
         */
        unbind : function(store){
            this.bindStore(null);
        },

        /**
         * Binds the paging toolbar to the specified {@link Ext.data.Store} <b>(deprecated)</b>
         * @param {Ext.data.Store} store The data store to bind
         */
        bind : function(store){
            this.bindStore(store);
        },

        // private
        onDestroy : function(){
            this.bindStore(null);
            Ext.PagingToolbar.superclass.onDestroy.call(this);
        }
    });

    })();
    Ext.reg('paging', Ext.PagingToolbar);