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	14
Bob Smith	Europe	Firefox	16
Carol White	Asia	Safari	8
David Brown	South America	Edge	14
Eva Green	Africa	Opera	58
Alice Johnson	North America	Chrome	14
Bob Smith	Europe	Firefox	30
Carol White	Asia	Safari	43
David Brown	South America	Edge	33
Eva Green	Africa	Opera	99
Alice Johnson	North America	Chrome	48
Bob Smith	Europe	Firefox	15
Carol White	Asia	Safari	11
David Brown	South America	Edge	30
Eva Green	Africa	Opera	47
Alice Johnson	North America	Chrome	74
Bob Smith	Europe	Firefox	90
Carol White	Asia	Safari	46
David Brown	South America	Edge	54
Eva Green	Africa	Opera	27
Alice Johnson	North America	Chrome	70
Bob Smith	Europe	Firefox	61
Carol White	Asia	Safari	25
David Brown	South America	Edge	57
Eva Green	Africa	Opera	68
Alice Johnson	North America	Chrome	96
Bob Smith	Europe	Firefox	56
Carol White	Asia	Safari	93
David Brown	South America	Edge	58
Eva Green	Africa	Opera	40
Alice Johnson	North America	Chrome	21
Bob Smith	Europe	Firefox	78
Carol White	Asia	Safari	74
David Brown	South America	Edge	13
Eva Green	Africa	Opera	6
Alice Johnson	North America	Chrome	38
Bob Smith	Europe	Firefox	79
Carol White	Asia	Safari	66
David Brown	South America	Edge	98
Eva Green	Africa	Opera	41
Alice Johnson	North America	Chrome	16
Bob Smith	Europe	Firefox	10
Carol White	Asia	Safari	91
David Brown	South America	Edge	20
Eva Green	Africa	Opera	44
Alice Johnson	North America	Chrome	70
Bob Smith	Europe	Firefox	46
Carol White	Asia	Safari	25
David Brown	South America	Edge	8
Eva Green	Africa	Opera	40
Alice Johnson	North America	Chrome	22
Bob Smith	Europe	Firefox	95
Carol White	Asia	Safari	94
David Brown	South America	Edge	55
Eva Green	Africa	Opera	58
Alice Johnson	North America	Chrome	39
Bob Smith	Europe	Firefox	84
Carol White	Asia	Safari	55
David Brown	South America	Edge	61
Eva Green	Africa	Opera	98

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.