React Example: Padding

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import React from 'react'
import * as ReactDOM from 'react-dom/client'

import './index.css'

import { useVirtualizer } from '@tanstack/react-virtual'

const rows = new Array(10000)
  .fill(true)
  .map(() => 25 + Math.round(Math.random() * 100))

const columns = new Array(10000)
  .fill(true)
  .map(() => 75 + Math.round(Math.random() * 100))

function App() {
  return (
    <div>
      <p>
        These components are using <strong>dynamic</strong> sizes. This means
        that each element's exact dimensions are unknown when rendered. An
        estimated dimension is used as the initial measurement, then this
        measurement is readjusted on the fly as each element is rendered.
      </p>
      <br />
      <br />

      <h3>Rows</h3>
      <RowVirtualizerDynamic rows={rows} />
      <br />
      <br />
      <h3>Columns</h3>
      <ColumnVirtualizerDynamic columns={columns} />
      <br />
      <br />
      <h3>Grid</h3>
      <GridVirtualizerDynamic rows={rows} columns={columns} />
    </div>
  )
}

function RowVirtualizerDynamic({ rows }: { rows: Array<number> }) {
  const parentRef = React.useRef<HTMLDivElement>(null)

  const rowVirtualizer = useVirtualizer({
    count: rows.length,
    getScrollElement: () => parentRef.current,
    estimateSize: () => 50,
    paddingStart: 100,
    paddingEnd: 100,
  })

  return (
    <>
      <div
        ref={parentRef}
        className="List"
        style={{
          height: `200px`,
          width: `400px`,
          overflow: 'auto',
        }}
      >
        <div
          style={{
            height: `${rowVirtualizer.getTotalSize()}px`,
            width: '100%',
            position: 'relative',
          }}
        >
          {rowVirtualizer.getVirtualItems().map((virtualRow) => (
            <div
              key={virtualRow.key}
              data-index={virtualRow.index}
              ref={rowVirtualizer.measureElement}
              className={virtualRow.index % 2 ? 'ListItemOdd' : 'ListItemEven'}
              style={{
                position: 'absolute',
                top: 0,
                left: 0,
                width: '100%',
                height: `${rows[virtualRow.index]}px`,
                transform: `translateY(${virtualRow.start}px)`,
              }}
            >
              Row {virtualRow.index}
            </div>
          ))}
        </div>
      </div>
    </>
  )
}

function ColumnVirtualizerDynamic({ columns }: { columns: Array<number> }) {
  const parentRef = React.useRef<HTMLDivElement>(null)

  const columnVirtualizer = useVirtualizer({
    horizontal: true,
    count: columns.length,
    getScrollElement: () => parentRef.current,
    estimateSize: () => 50,
    paddingStart: 100,
    paddingEnd: 100,
  })

  return (
    <>
      <div
        ref={parentRef}
        className="List"
        style={{
          width: `400px`,
          height: `100px`,
          overflow: 'auto',
        }}
      >
        <div
          style={{
            width: `${columnVirtualizer.getTotalSize()}px`,
            height: '100%',
            position: 'relative',
          }}
        >
          {columnVirtualizer.getVirtualItems().map((virtualColumn) => (
            <div
              key={virtualColumn.key}
              data-index={virtualColumn.index}
              ref={columnVirtualizer.measureElement}
              className={
                virtualColumn.index % 2 ? 'ListItemOdd' : 'ListItemEven'
              }
              style={{
                position: 'absolute',
                top: 0,
                left: 0,
                height: '100%',
                width: `${columns[virtualColumn.index]}px`,
                transform: `translateX(${virtualColumn.start}px)`,
              }}
            >
              Column {virtualColumn.index}
            </div>
          ))}
        </div>
      </div>
    </>
  )
}

function GridVirtualizerDynamic({
  rows,
  columns,
}: {
  rows: Array<number>
  columns: Array<number>
}) {
  const parentRef = React.useRef<HTMLDivElement>(null)

  const rowVirtualizer = useVirtualizer({
    count: rows.length,
    getScrollElement: () => parentRef.current,
    estimateSize: () => 50,
    paddingStart: 200,
    paddingEnd: 200,
    indexAttribute: 'data-row-index',
  })

  const columnVirtualizer = useVirtualizer({
    horizontal: true,
    count: columns.length,
    getScrollElement: () => parentRef.current,
    estimateSize: () => 50,
    paddingStart: 200,
    paddingEnd: 200,
    indexAttribute: 'data-column-index',
  })

  const [show, setShow] = React.useState(true)

  const halfWay = Math.floor(rows.length / 2)

  return (
    <>
      <button onClick={() => setShow((old) => !old)}>Toggle</button>
      <button onClick={() => rowVirtualizer.scrollToIndex(halfWay)}>
        Scroll to index {halfWay}
      </button>
      <button onClick={() => rowVirtualizer.scrollToIndex(rows.length - 1)}>
        Scroll to index {rows.length - 1}
      </button>
      {show ? (
        <div
          ref={parentRef}
          className="List"
          style={{
            height: `400px`,
            width: `500px`,
            overflow: 'auto',
          }}
        >
          <div
            style={{
              height: `${rowVirtualizer.getTotalSize()}px`,
              width: `${columnVirtualizer.getTotalSize()}px`,
              position: 'relative',
            }}
          >
            {rowVirtualizer.getVirtualItems().map((virtualRow) => (
              <React.Fragment key={virtualRow.key}>
                {columnVirtualizer.getVirtualItems().map((virtualColumn) => (
                  <div
                    key={virtualColumn.key}
                    data-row-index={virtualRow.index}
                    data-column-index={virtualColumn.index}
                    ref={(el) => {
                      rowVirtualizer.measureElement(el)
                      columnVirtualizer.measureElement(el)
                    }}
                    className={
                      virtualColumn.index % 2
                        ? virtualRow.index % 2 === 0
                          ? 'ListItemOdd'
                          : 'ListItemEven'
                        : virtualRow.index % 2
                          ? 'ListItemOdd'
                          : 'ListItemEven'
                    }
                    style={{
                      position: 'absolute',
                      top: 0,
                      left: 0,
                      width: `${columns[virtualColumn.index]}px`,
                      height: `${rows[virtualRow.index]}px`,
                      transform: `translateX(${virtualColumn.start}px) translateY(${virtualRow.start}px)`,
                    }}
                  >
                    Cell {virtualRow.index}, {virtualColumn.index}
                  </div>
                ))}
              </React.Fragment>
            ))}
          </div>
        </div>
      ) : null}
      <br />
      <br />
      {process.env.NODE_ENV === 'development' ? (
        <p>
          <strong>Notice:</strong> You are currently running React in
          development mode. Rendering performance will be slightly degraded
          until this application is built for production.
        </p>
      ) : null}
    </>
  )
}

ReactDOM.createRoot(document.getElementById('root')!).render(
  <React.StrictMode>
    <App />
  </React.StrictMode>,
)