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	34
Carol White	Asia	Safari	5
David Brown	South America	Edge	3
Eva Green	Africa	Opera	92
Alice Johnson	North America	Chrome	30
Bob Smith	Europe	Firefox	73
Carol White	Asia	Safari	65
David Brown	South America	Edge	40
Eva Green	Africa	Opera	38
Alice Johnson	North America	Chrome	2
Bob Smith	Europe	Firefox	2
Carol White	Asia	Safari	44
David Brown	South America	Edge	5
Eva Green	Africa	Opera	45
Alice Johnson	North America	Chrome	73
Bob Smith	Europe	Firefox	4
Carol White	Asia	Safari	76
David Brown	South America	Edge	59
Eva Green	Africa	Opera	32
Alice Johnson	North America	Chrome	39
Bob Smith	Europe	Firefox	74
Carol White	Asia	Safari	25
David Brown	South America	Edge	79
Eva Green	Africa	Opera	24
Alice Johnson	North America	Chrome	99
Bob Smith	Europe	Firefox	79
Carol White	Asia	Safari	77
David Brown	South America	Edge	89
Eva Green	Africa	Opera	25
Alice Johnson	North America	Chrome	18
Bob Smith	Europe	Firefox	98
Carol White	Asia	Safari	80
David Brown	South America	Edge	21
Eva Green	Africa	Opera	62
Alice Johnson	North America	Chrome	29
Bob Smith	Europe	Firefox	86
Carol White	Asia	Safari	68
David Brown	South America	Edge	45
Eva Green	Africa	Opera	18
Alice Johnson	North America	Chrome	13
Bob Smith	Europe	Firefox	63
Carol White	Asia	Safari	84
David Brown	South America	Edge	2
Eva Green	Africa	Opera	30
Alice Johnson	North America	Chrome	65
Bob Smith	Europe	Firefox	100
Carol White	Asia	Safari	50
David Brown	South America	Edge	7
Eva Green	Africa	Opera	53
Alice Johnson	North America	Chrome	50
Bob Smith	Europe	Firefox	37
Carol White	Asia	Safari	76
David Brown	South America	Edge	39
Eva Green	Africa	Opera	55
Alice Johnson	North America	Chrome	82
Bob Smith	Europe	Firefox	50
Carol White	Asia	Safari	51
David Brown	South America	Edge	74
Eva Green	Africa	Opera	30

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.