//create ext data store and grid.
var store = null;
var grid = null;

//set default scroll variables.
var currentpos = 0;
var currentpage = 1;

//set constants.
//itemsperpage: number of records that appear on each page of content.
var itemsperpage = 14;
//number of pages of content to fetch when offset reached.
var pagestofetch = 2;
//number of pixel interval to fire handler request.
var scrolloffset = 263;
var scrolloffsetinterval = 263;
    
//event fires when ext is loaded and ready to display controls.
Ext.onReady(function(){
    
    //set current count.
    var x = document.getElementById("currentcount");
    x.innerHTML = (itemsperpage*pagestofetch);
    
    //create reference to GetZipCodes.ashx
    var s = new GetZipCodes();
    
    //call GetZipCodes.ashx handler
    //to retrieve total records in collection.
    s.GetZipCodesCount(function(response) { 
        var x = document.getElementById("totalcount");
        x.innerHTML = response.result;
    });
    
    //set skip take values.
    var y = document.getElementById("skip1");
        y.innerHTML = '0';
    var z = document.getElementById("skip2");
        z.innerHTML = '0';
    var a = document.getElementById("take1");
        a.innerHTML = (itemsperpage * pagestofetch);
    var b = document.getElementById("take2");
        b.innerHTML = (itemsperpage * pagestofetch);
        
    //set ext state provider.
    Ext.state.Manager.setProvider(new Ext.state.CookieProvider());
    
    //initialize temp data store for handler response.
    var myData
    
    //call GetZipCodes.ashx to retrieve zip code data.
    s.GetZipCodesList(
    itemsperpage*pagestofetch,
    currentpage,
    function(response) { //async callback fires when handler returns data.
        //store response.
        myData = response;
        
        //create jason data store and load data.
        store = new Ext.data.JsonStore({data: myData,
                                        root: 'result',
                                        fields: ['zip', 
                                                 'city', 
                                                 'state', 
                                                 'latitude', 
                                                 'longitude', 
                                                 'timeZone', 
                                                 'dst']
                                        });
              
          
            //create the ext Grid and load data store
            grid = new Ext.grid.GridPanel({
                store: store,
                columns: [
                    {header: "Zip", width: 120, sortable: false, dataIndex: 'zip'},
                    {header: "City", width: 120, sortable: false, dataIndex: 'city'},
                    {header: "State", width: 120, sortable: false, dataIndex: 'state'},
                    {header: "Latitude", width: 120, sortable: false, dataIndex: 'latitude'},
                    {header: "Longitude", width: 120, sortable: false, dataIndex: 'longitude'},
                    {header: "Time Zone", width: 120, sortable: false, dataIndex: 'timeZone'},
                    {header: "DST", width: 120, sortable: false, dataIndex: 'dst'}
                ],
                stripeRows: true,
                height:350,
                autoExpandColumn:6,
                header: false,
                title:'Zip Code Listing'
            });
            //render grid
            grid.render('zip-grid');
            //add scroll event listener
            grid.addListener('bodyscroll',scrollListener);

        }); //end Json call listener.
          
   });  //end ext ready listener
       
//scrollListener
//fires when grid is scrolled.
function scrollListener(scrollLeft, scrollTop){
    //only handle scroll downs past highest position.
    if ( scrollTop > currentpos )
    {
        //check if we should get more data
        if ( scrollTop >  scrolloffset )
        {
            //store current grid scroll state.
            var state = grid.getView().getScrollState();
            
            //adjust scroll offset
            scrolloffset=scrollTop+scrolloffsetinterval;
            //adjust current page
            currentpage=currentpage+1;
            
            //initialize temp data store for handler response.
            var myData
            //call GetZipCodes.ashx to retrieve zip code data for next pages of data
            var s = new GetZipCodes();
            s.GetZipCodesList(
            itemsperpage*pagestofetch,
            currentpage,
            function(response) {  //async callback fires when handler returns data.
                //store response.
                myData = response;
                //append items to json store.
                store.loadData(myData,true);
                    
                //restore grid scroll state.
                grid.getView().restoreScroll(state);
                
                //set current count.
                var x = document.getElementById("currentcount");
                x.innerHTML = store.getCount();
                
                //set skip take values.
                var y = document.getElementById("skip1");
                    y.innerHTML = (((currentpage-1) * pagestofetch) * itemsperpage);
                var z = document.getElementById("skip2");
                    z.innerHTML = (((currentpage-1) * pagestofetch) * itemsperpage);
                var a = document.getElementById("take1");
                    a.innerHTML = (itemsperpage * pagestofetch);
                var b = document.getElementById("take2");
                    b.innerHTML = (itemsperpage * pagestofetch);
                
                 }); //end: async callback fires when handler returns data.
                 
        }  //end: check if we should get more data
        
        //reset current scroll position
        currentpos=scrollTop;
        
    } //end last position test.
    
} //end: scrollListener
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