From react-window to react-virtual

The tremendous Tanner Linsley recently released react-virtual. react-virtual provides "hooks for virtualizing scrollable elements in React".

I was already using the (also excellent) react-window for this purpose. react-window does the virtualising job and does it very well indeed However, I was both intrigued by the lure of the new shiny thing. I've also never been the biggest fan of react-window's API. So I tried switching over from react-window to react-virtual as an experiment. To my delight, the experiment went so well I didn't look back!

What did I get out of the switch?

• Simpler code / nicer developer ergonomics. The API for react-virtual allowed me to simplify my code and lose a layer of components.
• TypeScript support in the box
• Improved perceived performance. I didn't run any specific tests to quantify this, but I can say that the same functionality now feels snappier.

I tweeted my delight at this and Tanner asked if there was commit diff I could share. I couldn't as it's a private codebase, but I thought it could form the basis of a blogpost.

Nice! Do you have a commit diff we could see?

— Tanner Linsley ⚛️ (@tannerlinsley) May 10, 2020

In case you hadn't guessed, this is that blog post...

Make that change

So what does the change look like? Well first remove react-window from your project:

yarn remove react-window @types/react-window

Add the dependency to react-virtual:

yarn add react-virtual

Change your imports from:

import { FixedSizeList, ListChildComponentProps } from 'react-window';

to:

import { useVirtual } from 'react-virtual';

Change your component code from:

type ImportantDataListProps = {
  classes: ReturnType<typeof useStyles>;
  importants: ImportantData[];
};

const ImportantDataList: React.FC<ImportantDataListProps> = React.memo(
  (props) => (
    <FixedSizeList
      height={400}
      width={'100%'}
      itemSize={80}
      itemCount={props.importants.length}
      itemData={props}
    >
      {RenderRow}
    </FixedSizeList>
  ),
);

type ListItemProps = {
  classes: ReturnType<typeof useStyles>;
  importants: ImportantData[];
};

function RenderRow(props: ListChildComponentProps) {
  const { index, style } = props;
  const { importants, classes } = props.data as ListItemProps;
  const important = importants[index];

  return (
    <ListItem button style={style} key={index}>
      <ImportantThing classes={classes} important={important} />
    </ListItem>
  );
}

Of the above you can delete the ListItemProps type and the associate RenderRow function. You won't need them again! There's no longer a need to pass down data to the child element and then extract it for usage; it all comes down into a single simpler component.

Replace the ImportantDataList component with this:

const ImportantDataList: React.FC<ImportantDataListProps> = React.memo(
  (props) => {
    const parentRef = React.useRef<HTMLDivElement>(null);

    const rowVirtualizer = useVirtual({
      size: props.importants.length,
      parentRef,
      estimateSize: React.useCallback(() => 80, []), // This is just a best guess
      overscan: 5,
    });

    return (
      <div
        ref={parentRef}
        style={{
          width: `100%`,
          height: `500px`,
          overflow: 'auto',
        }}
      >
        <div
          style={{
            height: `${rowVirtualizer.totalSize}px`,
            width: '100%',
            position: 'relative',
          }}
        >
          {rowVirtualizer.virtualItems.map((virtualRow) => (
            <div
              key={virtualRow.index}
              ref={virtualRow.measureRef}
              className={props.classes.hoverRow}
              style={{
                position: 'absolute',
                top: 0,
                left: 0,
                width: '100%',
                height: `${virtualRow.size}px`,
                transform: `translateY(${virtualRow.start}px)`,
              }}
            >
              <ImportantThing
                classes={props.classes}
                important={props.importants[virtualRow.index]}
              />
            </div>
          ))}
        </div>
      </div>
    );
  },
);

And you are done! Thanks Tanner for this tremendous library!