Viewed Data Service

Overview

ViewedDataService tracks which dataIds have been marked as viewed in the current session. Internally it stores ids in a Set<string> and publishes a single event whenever viewed state changes.

Typical usage is to:

• mark a data item as viewed when users land on a slice
• query whether a data item has been viewed to seed UI state
• subscribe to viewed changes for incremental updates
• clear viewed state when a context reset is needed

Events

The following events are published by ViewedDataService.

Event	Description
VIEWED_DATA_CHANGED	Fired when one data item is newly marked viewed, or when all viewed data is cleared.

Event payload

type ViewedDataPayload = {
  viewedDataId?: string;
  viewedDataCleared?: boolean;
};

• When a single data item is marked viewed: { viewedDataId: string }
• When all viewed data is cleared: { viewedDataCleared: true }

API

• markDataViewed(dataId: string): void

  Marks one data item as viewed and emits VIEWED_DATA_CHANGED only if:

  • dataId is truthy, and
  • it was not already marked viewed.

• isDataViewed(dataId: string): boolean

  Returns true if dataId is currently in the viewed set.

• clearViewedData(): void

  Clears all viewed dataIds and emits VIEWED_DATA_CHANGED with { viewedDataCleared: true }.

• subscribeViewedDataChanges(listener): Subscription

  Subscribes to VIEWED_DATA_CHANGED payloads.

  const subscription = viewedDataService.subscribeViewedDataChanges(payload => {
    if (payload.viewedDataCleared) {
      // reset local viewed state
      return;
    }
  
    if (payload.viewedDataId) {
      // mark one data item as viewed locally
    }
  });
  
  // later
  subscription.unsubscribe();

Notes

• Service registration name: viewedDataService
• Alternate registration name: ViewedDataService
• The service is session-scoped in-memory state; it is not persisted by default.