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	56
Bob Smith	Europe	Firefox	62
Carol White	Asia	Safari	8
David Brown	South America	Edge	49
Eva Green	Africa	Opera	44
Alice Johnson	North America	Chrome	21
Bob Smith	Europe	Firefox	5
Carol White	Asia	Safari	75
David Brown	South America	Edge	73
Eva Green	Africa	Opera	70
Alice Johnson	North America	Chrome	94
Bob Smith	Europe	Firefox	51
Carol White	Asia	Safari	73
David Brown	South America	Edge	59
Eva Green	Africa	Opera	51
Alice Johnson	North America	Chrome	12
Bob Smith	Europe	Firefox	26
Carol White	Asia	Safari	41
David Brown	South America	Edge	8
Eva Green	Africa	Opera	19
Alice Johnson	North America	Chrome	17
Bob Smith	Europe	Firefox	5
Carol White	Asia	Safari	24
David Brown	South America	Edge	82
Eva Green	Africa	Opera	32
Alice Johnson	North America	Chrome	67
Bob Smith	Europe	Firefox	61
Carol White	Asia	Safari	23
David Brown	South America	Edge	71
Eva Green	Africa	Opera	5
Alice Johnson	North America	Chrome	69
Bob Smith	Europe	Firefox	28
Carol White	Asia	Safari	53
David Brown	South America	Edge	69
Eva Green	Africa	Opera	96
Alice Johnson	North America	Chrome	74
Bob Smith	Europe	Firefox	76
Carol White	Asia	Safari	72
David Brown	South America	Edge	49
Eva Green	Africa	Opera	31
Alice Johnson	North America	Chrome	3
Bob Smith	Europe	Firefox	69
Carol White	Asia	Safari	30
David Brown	South America	Edge	85
Eva Green	Africa	Opera	27
Alice Johnson	North America	Chrome	83
Bob Smith	Europe	Firefox	90
Carol White	Asia	Safari	77
David Brown	South America	Edge	100
Eva Green	Africa	Opera	55
Alice Johnson	North America	Chrome	42
Bob Smith	Europe	Firefox	13
Carol White	Asia	Safari	79
David Brown	South America	Edge	83
Eva Green	Africa	Opera	77
Alice Johnson	North America	Chrome	65
Bob Smith	Europe	Firefox	49
Carol White	Asia	Safari	12
David Brown	South America	Edge	94
Eva Green	Africa	Opera	27

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.