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	19
Bob Smith	Europe	Firefox	22
Carol White	Asia	Safari	76
David Brown	South America	Edge	48
Eva Green	Africa	Opera	74
Alice Johnson	North America	Chrome	74
Bob Smith	Europe	Firefox	95
Carol White	Asia	Safari	48
David Brown	South America	Edge	33
Eva Green	Africa	Opera	46
Alice Johnson	North America	Chrome	52
Bob Smith	Europe	Firefox	74
Carol White	Asia	Safari	6
David Brown	South America	Edge	30
Eva Green	Africa	Opera	3
Alice Johnson	North America	Chrome	64
Bob Smith	Europe	Firefox	18
Carol White	Asia	Safari	3
David Brown	South America	Edge	10
Eva Green	Africa	Opera	66
Alice Johnson	North America	Chrome	52
Bob Smith	Europe	Firefox	2
Carol White	Asia	Safari	29
David Brown	South America	Edge	8
Eva Green	Africa	Opera	39
Alice Johnson	North America	Chrome	86
Bob Smith	Europe	Firefox	45
Carol White	Asia	Safari	77
David Brown	South America	Edge	37
Eva Green	Africa	Opera	89
Alice Johnson	North America	Chrome	4
Bob Smith	Europe	Firefox	91
Carol White	Asia	Safari	2
David Brown	South America	Edge	11
Eva Green	Africa	Opera	16
Alice Johnson	North America	Chrome	79
Bob Smith	Europe	Firefox	67
Carol White	Asia	Safari	77
David Brown	South America	Edge	25
Eva Green	Africa	Opera	71
Alice Johnson	North America	Chrome	90
Bob Smith	Europe	Firefox	35
Carol White	Asia	Safari	8
David Brown	South America	Edge	89
Eva Green	Africa	Opera	12
Alice Johnson	North America	Chrome	13
Bob Smith	Europe	Firefox	5
Carol White	Asia	Safari	61
David Brown	South America	Edge	8
Eva Green	Africa	Opera	75
Alice Johnson	North America	Chrome	3
Bob Smith	Europe	Firefox	10
Carol White	Asia	Safari	45
David Brown	South America	Edge	60
Eva Green	Africa	Opera	51
Alice Johnson	North America	Chrome	87
Bob Smith	Europe	Firefox	25
Carol White	Asia	Safari	76
David Brown	South America	Edge	25
Eva Green	Africa	Opera	97

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.