Buffering

import { Grid } from 'cx/widgets';

Grid supports buffered rendering which dramatically improves performance with large datasets. Instead of rendering all rows, only visible rows plus a buffer are rendered, enabling smooth scrolling with thousands of records.

 <div controller={PageController}>
  <Grid
    records={m.records}
    keyField="id"
    buffered
    style="height: 400px"
    mod={["fixed-layout", "contain"]}
    cached
    selection={{ type: KeySelection, bind: m.selection }}
    columns={[
      {
        header: "#",
        align: "center",
        children: <div class="cxe-grid-row-number" />,
        defaultWidth: 70,
      },
      {
        header: { text: "Name", style: "width: 100%" },
        field: "fullName",
        sortable: true,
        resizable: true,
      },
      {
        header: "Continent",
        field: "continent",
        sortable: true,
        resizable: true,
        defaultWidth: 130,
      },
      {
        header: "Browser",
        field: "browser",
        sortable: true,
        resizable: true,
        defaultWidth: 100,
      },
      {
        header: "Visits",
        field: "visits",
        sortable: true,
        align: "right",
        resizable: true,
        defaultWidth: 70,
      },
    ]}
  />
</div> 
 class PageController extends Controller {
  onInit() {
    this.store.init(
      m.records,
      Array.from({ length: 5000 }, (_, i) => ({
        id: i + 1,
        fullName: names[i % 5],
        continent: continents[i % 5],
        browser: browsers[i % 5],
        visits: Math.floor(Math.random() * 100) + 1,
      })),
    );
  }
} 
 interface Record {
  id: number;
  fullName: string;
  continent: string;
  browser: string;
  visits: number;
}

interface PageModel {
  records: Record[];
  selection: number;
}

const m = createModel<PageModel>(); 
 import { createModel } from "cx/data";
import { Controller, KeySelection } from "cx/ui";
import { Grid } from "cx/widgets"; 

Name	Continent	Browser	Visits
Alice Johnson	North America	Chrome	16
Bob Smith	Europe	Firefox	95
Carol White	Asia	Safari	1
David Brown	South America	Edge	11
Eva Green	Africa	Opera	53
Alice Johnson	North America	Chrome	17
Bob Smith	Europe	Firefox	79
Carol White	Asia	Safari	82
David Brown	South America	Edge	56
Eva Green	Africa	Opera	14
Alice Johnson	North America	Chrome	77
Bob Smith	Europe	Firefox	97
Carol White	Asia	Safari	32
David Brown	South America	Edge	52
Eva Green	Africa	Opera	66
Alice Johnson	North America	Chrome	88
Bob Smith	Europe	Firefox	65
Carol White	Asia	Safari	35
David Brown	South America	Edge	28
Eva Green	Africa	Opera	3
Alice Johnson	North America	Chrome	12
Bob Smith	Europe	Firefox	10
Carol White	Asia	Safari	63
David Brown	South America	Edge	6
Eva Green	Africa	Opera	46
Alice Johnson	North America	Chrome	26
Bob Smith	Europe	Firefox	43
Carol White	Asia	Safari	21
David Brown	South America	Edge	32
Eva Green	Africa	Opera	66
Alice Johnson	North America	Chrome	24
Bob Smith	Europe	Firefox	11
Carol White	Asia	Safari	14
David Brown	South America	Edge	61
Eva Green	Africa	Opera	50
Alice Johnson	North America	Chrome	48
Bob Smith	Europe	Firefox	3
Carol White	Asia	Safari	51
David Brown	South America	Edge	46
Eva Green	Africa	Opera	65
Alice Johnson	North America	Chrome	69
Bob Smith	Europe	Firefox	26
Carol White	Asia	Safari	96
David Brown	South America	Edge	45
Eva Green	Africa	Opera	56
Alice Johnson	North America	Chrome	50
Bob Smith	Europe	Firefox	90
Carol White	Asia	Safari	3
David Brown	South America	Edge	6
Eva Green	Africa	Opera	30
Alice Johnson	North America	Chrome	35
Bob Smith	Europe	Firefox	54
Carol White	Asia	Safari	69
David Brown	South America	Edge	65
Eva Green	Africa	Opera	26
Alice Johnson	North America	Chrome	22
Bob Smith	Europe	Firefox	14
Carol White	Asia	Safari	16
David Brown	South America	Edge	68
Eva Green	Africa	Opera	99

This grid contains 5,000 rows but renders smoothly thanks to buffered mode. Try scrolling and sorting to see the performance.

How It Works

Enable buffered mode by setting the buffered property. The grid calculates which rows are visible and renders only those plus a configurable buffer for smooth scrolling.

<Grid
  records={m.records}
  buffered
  style="height: 400px"
  mod={["fixed-layout", "contain"]}
  cached
  columns={columns}
/>

For optimal performance, combine buffering with:

Fixed height - The grid needs a fixed height to calculate visible rows
mod="fixed-layout" - Uses CSS table-layout: fixed for faster rendering
mod="contain" - Adds CSS containment for better browser optimization
cached - Prevents row re-renders when unrelated store data changes

Row Numbers

Use the built-in cxe-grid-row-number class to display automatic row numbers:

{
  header: "#",
  defaultWidth: 50,
  children: <div class="cxe-grid-row-number" />
}

Configuration

Property	Type	Description
`buffered`	`boolean`	Enables buffered rendering mode.
`bufferSize`	`number`	Number of rows to render outside the visible area. Default is `60`.
`bufferStep`	`number`	Number of rows to add/remove when scrolling. Default is `15`.
`cached`	`boolean`	Prevents row re-renders when unrelated store data changes. Rows only update when their record data changes.
`lockColumnWidths`	`boolean`	Locks column widths to prevent layout shifts during scrolling.
`lockColumnWidthsRequiredRowCount`	`number`	Minimum number of rows required before column widths are locked.
`measureRowsOnScroll`	`boolean`	Re-measures row heights while scrolling. Useful for variable height rows.