[Feature Suggestion] Expose onItemsRendered value as props to rendered cells

I have a specific use-case*, that i need to know the value that i would get from onItemsRendered The thing is, the onItemsRendered callback is called only after the items was rendered.

I assume that, when render calls are made to render cells, the library already knows the values it will pass to onItemsRendered. as it uses them to calculate which cells to render.

So, the lib can pass it as an additional prop to the cell component.

• My use case is: I’m trying to build a grid with fixed header, footer, and left-most visual column.

Code example of what i need: https://github.com/bvaughn/react-window/compare/master...Bnaya:iterations?expand=1 I’n going to try and see if its helps me

[bvaughn]

Aside of that, i still think its possible to implement areEqual is way that ignores overscan…Index values and treats them as never changed, but the developer can opt-in to it.

It could be implemented that way, but I’m not comfortable wit treating something that changes as though it doesn’t change. I think it could lead to broken/unexpected behavior. The reason this is okay with style is that it only changes shallowly but that would not be the case with the indices you’re describing.

I think we’re going in a circles a little at this point. 😄 If you’d like to create a PR for me to consider, I will make time to look at it. (Can’t promise it will be merged, but I will look at it.)

[Bnaya]

My goal: I need to give special behaviour to the first and last rendered cells vertical and horizontal. The way i can tell that a cell is first/last is comparing item.rowIndex === item.itemsRenderedCallbackParams.overscanRowStartIndex

The idea is: even tho cell X,Y is changing, rowIndex === overscanRowStartIndex, I give it a named key, first-in-column:first-in-row, first-in-column:1-in-row etc. That’s only if its a “special” cell. And that’s how react uses the same DOM element even that the X,Y is different.

Let’s say i don’t have overscanRowStartIndex data as props, i can play with the key to force re-mount my edges cells by adding also x and y to the named key, something like: first-in-column-4:first-in-row-5. it will be less performant for me, but i think its reasonable.

Please see my itemKeyProvider: https://github.com/Bnaya/sticky-eurovision/blob/master/src/implementations/WithReactWindowAndSticky/WithReactWindowAndSticky.tsx#L50-L86 itemKey I hope it will be more clear

Aside of that, i still think its possible to implement areEqual is way that ignores overscan...Index values and treats them as never changed, but the developer can opt-in to it. Something like:

export default function areEqual(
  prevProps: Object,
  nextProps: Object
): boolean {
  const { overScanInfo: prevOverScanInfo, style: prevStyle, ...prevRest } = prevProps;
  const { overScanInfo: nextOverScanInfo, style: nextStyle, ...nextRest } = nextProps;

  // we don't care about you by default!!! 
  // shallowDiffers(prevOverScanInfo, nextOverScanInfo)

  return (
    !shallowDiffers(prevStyle, nextStyle) && !shallowDiffers(prevRest, nextRest)
  );
}