Type Safety Issue with `useOverlayData()` Return Type

[SaeWooKKang]

Problem

The useOverlayData() function currently returns Record<string, OverlayItem>, but since the key type is string, accessing with an incorrect string key returns undefined at runtime while TypeScript still infers the return type as OverlayItem.

This leads to runtime errors that could be prevented at compile time.

const overlayData = useOverlayData() 
const d = overlayData['wrongId'] // type: OverlayItem, runtime: undefined

It would be beneficial to make users aware at compile time that the value could be undefined.

Current Issue with Simple Type Union

If we simply add undefined to the value type, it achieves the initial goal of having the value type as OverlayItem | undefined:

export function createOverlaySafeContext() {
  const [OverlayContextProvider, useOverlayContext] = createSafeContext<OverlayData>('overlay-kit/OverlayContext');
 
  // ...others

  function useOverlayData(): Record<string, OverlayItem | undefined> {
    return useOverlayContext().overlayData;
  }

  return { OverlayContextProvider, useCurrentOverlay, useOverlayData };
}

However, this creates an issue with Object.values(overlayData) usage, where the return type becomes (OverlayItem | undefined)[] even though undefined never actually exists as an array element.

Suggestion

I believe a change to the useOverlayData interface is necessary.

If we change the implementation from object literal ({}) to Map, this issue could be resolved:

map.get('id') // type: OverlayItem | undefined
[...map.values()] // type: OverlayItem[]

Proposal: Use Map internally while exposing ReadonlyMap externally.

If you have a better opinion, please let me know. Thank you always.

[irhdab]

Hi! I'd like to work on this issue.

After reviewing the code, I agree with your proposal to use Map internally and expose ReadonlyMap externally. This approach will:

1. Provide proper type safety with .get() returning OverlayItem | undefined
2. Keep .values() clean, returning OverlayItem[] without undefined
3. Maintain backward compatibility for most use cases

The main changes would be in:

• packages/src/context/reducer.ts: Change overlayData from Record<OverlayId, OverlayItem> to Map<OverlayId, OverlayItem>
• Update all reducer functions to use Map methods (.get(), .set(), .delete())
• packages/src/context/context.ts: Update useOverlayData() return type to ReadonlyMap<string, OverlayItem>

Let me know if you'd like me to proceed with this implementation!