TCA-590 use swr for data fetching in learn -> TCA-586

[vas3a]

https://topcoder.atlassian.net/browse/TCA-590

Uses swr package to make the fetching requests for the learn tool.

• This ensures data is readily available on subsequent calls and it will be fetched in the background.
• It uses a localStorage caching for data that doesn't change too much (eg. all certificates listing, courses, lessons) so they are available on hard reloads as well.
• This doesn't affect the initial loading speeds (other than deduplicating calls), but improves the overall app responsiveness after the first use

[testflyjets]

This all looks great but it's not clear to me what the mechanism is to invalidate the client-side data caches if we update data in DynamoDB. Can you clarify that for me?

[brooketopcoder]

Looks good to me, but I am also curious about how the cache is invalidated. Is it related to the revalidateInMount config option? What mechanism does it use to revalidate? Does it just make the call again in the bg?

https://swr.vercel.app/docs/options

https://swr.vercel.app/docs/revalidation

[testflyjets]

This all looks great but it's not clear to me what the mechanism is to invalidate the client-side data caches if we update data in DynamoDB. Can you clarify that for me?

Ah, I think I get it -- SWR == "stale while refreshing" -- the cached data is provided while fresh data is retrieved in the background. All good.

[vas3a]

Hey @testflyjets @brooketopcoder ! Yeah, the cached data is served while the new data is fetched in the background.