This SO comment links to the best demonstration of off-by-one errors for laypeople I think I've ever run into.

(Though, admittedly, the "coming second" and "coming first" terminology was new to me...)

Here's the video that comment linked to:

Labels: development, logic, obo

// Call createGrid from Ext.onReady() to render the simple grid
// to a div with id of 'divUiHook2'.
function createGrid()   {
        
        //==============================================
        // code from Listing 7.1
        //==============================================
        var arrayData = [
                ['Jay Garcia',    'MD'],
                ['Aaron Baker',   'VA'],
                ['Susan Smith',   'DC'],
                ['Mary Stein',    'DE'],
                ['Bryan Shanley', 'NJ'],
                ['Nyri Selgado',  'CA']
        ];


        var nameRecord = Ext.data.Record.create([
                { name:'name',mapping:0},
                { name:'state',mapping:1}
        ]);

        var memoryProxy = new Ext.data.MemoryProxy(arrayData);
        var arrayReader = new Ext.data.ArrayReader({ id:0 },nameRecord);

        var store = new Ext.data.Store({
                reader:arrayReader,
                proxy:memoryProxy
        });

        store.load();                   // this was missing -mfn
        console.log(store.getCount());  // this is what clued me in -mfn


        //==============================================
        // code from Building_our_simple_gridpanel.html
        //==============================================
        var cm = new Ext.grid.ColumnModel([                          // 1
                {
                        header    : 'Full Name',
                        sortable  : true,
                        
                        // changed this from fullName
                        dataIndex : 'name'         // 2
                },
                {
                        header    : 'State',
                        dataIndex : 'state'
                }
        ]);

        var gridView = new Ext.grid.GridView();                     // 3
        var selModel = new Ext.grid.RowSelectionModel({             // 4
                singleSelect : true
        });

        var dummyGrid = new Ext.grid.GridPanel({                         // 5
                renderTo   : 'divUiHook2',      // changed from getBody.
                //autoHeight : true,            // replace with constant
                height     : 200,               // constant height
                width      : 250,
                store      : store,                                    // 6
                view       : gridView,                                 // 7
                colModel   : cm,                                       // 8
                selModel   : selModel,

                title      : 'Our first grid'
        });
}       // eo fn createGrid 

Labels: code, ExtJS, obo, problem solved