PnPjs is a powerful library for working with SharePoint, Microsoft Graph, and Office 365 APIs. While its built-in caching capabilities can significantly improve application performance, they can also introduce challenging debugging scenarios when data does not refresh as expected. This article examines common caching issues in PnP.js and offers solutions for identifying and resolving them.
A Brief Overview of PnPjs Caching
PnPjs implements caching at multiple levels to reduce network requests and enhance performance. The library uses a flexible caching system that can store data in memory, session storage, or local storage.
For a more detailed understanding of PnPjs caching, please refer to my previous article:
https://www.c-sharpcorner.com/article/enhancing-sharepoint-performance-using-pnpjs-caching/
Common Caching Issues
1. Stale Data Being Returned
Data appears outdated after changes in SharePoint.
Most common cause: cache is still valid and serving old results.
Fix
Reduce the expiry value.
Use a cache-busting strategy (e.g., unique keys or timestamps).
2. Cache Not Invalidated After List Item Changes
You may perform a .add() or .update(), but .get() still returns old data.
Fix
Manually invalidate or clear cache using:
import { getClient } from "@pnp/queryable";
const client = getClient(sp);
client.clear("my-list-items");
Alternatively, bypass caching for the next request:
await sp.web.lists.getByTitle("MyList").items(); // no .using(Caching())
3. Conflicting Cache Keys
Multiple queries use the same key and overwrite each other.
Fix
Use unique cache keys per query structure:
key: my-list-items-page-${pageNumber}
4. Issues in SPFx Contexts
Sometimes PnPjs caching doesn’t behave as expected in SPFx components (e.g., web parts reloading unexpectedly).
Fix
Ensure SPFx(this.context) is set correctly during initialization.
Avoid sharing spfi instance across isolated components if caching strategies differ.
Best Practices for Using PnPjs Caching
Always name your cache keys clearly and avoid collisions.
Implement manual cache invalidation after add/update/delete operations.
Use logging during development to monitor what is cached.
Consider a custom cache provider if you need more control.
Conclusion
PnPjs caching is a powerful feature that requires careful configuration and understanding. By recognizing common patterns of caching issues, implementing proper debugging techniques, and following best practices, you can leverage caching to improve performance while avoiding the pitfalls of stale data and difficult-to-debug behavior.
Remember that caching is a trade-off between performance and data freshness. Always consider your application's specific requirements and adjust your caching strategy accordingly. When in doubt, start with minimal caching and add it incrementally as you identify performance bottlenecks.