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	67
Bob Smith	Europe	Firefox	79
Carol White	Asia	Safari	73
David Brown	South America	Edge	87
Eva Green	Africa	Opera	81
Alice Johnson	North America	Chrome	2
Bob Smith	Europe	Firefox	63
Carol White	Asia	Safari	32
David Brown	South America	Edge	13
Eva Green	Africa	Opera	34
Alice Johnson	North America	Chrome	75
Bob Smith	Europe	Firefox	34
Carol White	Asia	Safari	90
David Brown	South America	Edge	69
Eva Green	Africa	Opera	5
Alice Johnson	North America	Chrome	72
Bob Smith	Europe	Firefox	30
Carol White	Asia	Safari	57
David Brown	South America	Edge	9
Eva Green	Africa	Opera	33
Alice Johnson	North America	Chrome	58
Bob Smith	Europe	Firefox	48
Carol White	Asia	Safari	94
David Brown	South America	Edge	90
Eva Green	Africa	Opera	58
Alice Johnson	North America	Chrome	20
Bob Smith	Europe	Firefox	90
Carol White	Asia	Safari	74
David Brown	South America	Edge	23
Eva Green	Africa	Opera	49
Alice Johnson	North America	Chrome	50
Bob Smith	Europe	Firefox	25
Carol White	Asia	Safari	81
David Brown	South America	Edge	9
Eva Green	Africa	Opera	100
Alice Johnson	North America	Chrome	50
Bob Smith	Europe	Firefox	47
Carol White	Asia	Safari	25
David Brown	South America	Edge	93
Eva Green	Africa	Opera	93
Alice Johnson	North America	Chrome	99
Bob Smith	Europe	Firefox	58
Carol White	Asia	Safari	9
David Brown	South America	Edge	77
Eva Green	Africa	Opera	11
Alice Johnson	North America	Chrome	86
Bob Smith	Europe	Firefox	46
Carol White	Asia	Safari	20
David Brown	South America	Edge	68
Eva Green	Africa	Opera	62
Alice Johnson	North America	Chrome	34
Bob Smith	Europe	Firefox	49
Carol White	Asia	Safari	41
David Brown	South America	Edge	55
Eva Green	Africa	Opera	97
Alice Johnson	North America	Chrome	98
Bob Smith	Europe	Firefox	69
Carol White	Asia	Safari	6
David Brown	South America	Edge	75
Eva Green	Africa	Opera	66

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.