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	65
Bob Smith	Europe	Firefox	48
Carol White	Asia	Safari	37
David Brown	South America	Edge	48
Eva Green	Africa	Opera	65
Alice Johnson	North America	Chrome	98
Bob Smith	Europe	Firefox	50
Carol White	Asia	Safari	78
David Brown	South America	Edge	54
Eva Green	Africa	Opera	41
Alice Johnson	North America	Chrome	67
Bob Smith	Europe	Firefox	31
Carol White	Asia	Safari	22
David Brown	South America	Edge	55
Eva Green	Africa	Opera	40
Alice Johnson	North America	Chrome	35
Bob Smith	Europe	Firefox	5
Carol White	Asia	Safari	66
David Brown	South America	Edge	11
Eva Green	Africa	Opera	55
Alice Johnson	North America	Chrome	6
Bob Smith	Europe	Firefox	81
Carol White	Asia	Safari	16
David Brown	South America	Edge	5
Eva Green	Africa	Opera	90
Alice Johnson	North America	Chrome	22
Bob Smith	Europe	Firefox	93
Carol White	Asia	Safari	37
David Brown	South America	Edge	50
Eva Green	Africa	Opera	24
Alice Johnson	North America	Chrome	94
Bob Smith	Europe	Firefox	39
Carol White	Asia	Safari	56
David Brown	South America	Edge	42
Eva Green	Africa	Opera	97
Alice Johnson	North America	Chrome	29
Bob Smith	Europe	Firefox	50
Carol White	Asia	Safari	48
David Brown	South America	Edge	46
Eva Green	Africa	Opera	30
Alice Johnson	North America	Chrome	65
Bob Smith	Europe	Firefox	16
Carol White	Asia	Safari	64
David Brown	South America	Edge	78
Eva Green	Africa	Opera	21
Alice Johnson	North America	Chrome	76
Bob Smith	Europe	Firefox	93
Carol White	Asia	Safari	45
David Brown	South America	Edge	63
Eva Green	Africa	Opera	100
Alice Johnson	North America	Chrome	73
Bob Smith	Europe	Firefox	47
Carol White	Asia	Safari	54
David Brown	South America	Edge	47
Eva Green	Africa	Opera	63
Alice Johnson	North America	Chrome	15
Bob Smith	Europe	Firefox	75
Carol White	Asia	Safari	60
David Brown	South America	Edge	45
Eva Green	Africa	Opera	95

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.