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	10
Bob Smith	Europe	Firefox	44
Carol White	Asia	Safari	48
David Brown	South America	Edge	9
Eva Green	Africa	Opera	76
Alice Johnson	North America	Chrome	62
Bob Smith	Europe	Firefox	9
Carol White	Asia	Safari	88
David Brown	South America	Edge	47
Eva Green	Africa	Opera	11
Alice Johnson	North America	Chrome	11
Bob Smith	Europe	Firefox	97
Carol White	Asia	Safari	81
David Brown	South America	Edge	53
Eva Green	Africa	Opera	35
Alice Johnson	North America	Chrome	25
Bob Smith	Europe	Firefox	13
Carol White	Asia	Safari	51
David Brown	South America	Edge	67
Eva Green	Africa	Opera	58
Alice Johnson	North America	Chrome	5
Bob Smith	Europe	Firefox	79
Carol White	Asia	Safari	89
David Brown	South America	Edge	70
Eva Green	Africa	Opera	75
Alice Johnson	North America	Chrome	95
Bob Smith	Europe	Firefox	51
Carol White	Asia	Safari	34
David Brown	South America	Edge	88
Eva Green	Africa	Opera	60
Alice Johnson	North America	Chrome	7
Bob Smith	Europe	Firefox	30
Carol White	Asia	Safari	19
David Brown	South America	Edge	3
Eva Green	Africa	Opera	7
Alice Johnson	North America	Chrome	11
Bob Smith	Europe	Firefox	92
Carol White	Asia	Safari	39
David Brown	South America	Edge	22
Eva Green	Africa	Opera	18
Alice Johnson	North America	Chrome	24
Bob Smith	Europe	Firefox	48
Carol White	Asia	Safari	86
David Brown	South America	Edge	85
Eva Green	Africa	Opera	94
Alice Johnson	North America	Chrome	1
Bob Smith	Europe	Firefox	10
Carol White	Asia	Safari	44
David Brown	South America	Edge	72
Eva Green	Africa	Opera	55
Alice Johnson	North America	Chrome	70
Bob Smith	Europe	Firefox	56
Carol White	Asia	Safari	13
David Brown	South America	Edge	42
Eva Green	Africa	Opera	66
Alice Johnson	North America	Chrome	96
Bob Smith	Europe	Firefox	81
Carol White	Asia	Safari	49
David Brown	South America	Edge	37
Eva Green	Africa	Opera	82

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.