Docs: Updating guides on PPR and ISR (#81307)
The PR fixes issues in two different guides.
### PPR
In PPR, the code for jsx and tsx versions should use the language
switcher. Currently, these are displayed below each other in the guide
which seems unintentional.
### ISR
This change fixes multiple issues:
**fixes in the example:**
the example currently does not match the text below (_Here's how this
example works:_). It says:
> If /blog/26 is requested, Next.js will generate and cache this page
on-demand
that is of course not correct because there are only 25 blog posts
returned from the API. No blog post data is returned for `/blog/26`,
making this example wrong and confusing.
By slicing the posts and supplying only 24 of 25 blog posts for static
generation during the build process, the guide becomes much more
explicit - the 25th blog post can be used for inspecting the workings of
the on-the-fly generation and caching. Turning `dynamicParams` to
`false` or `true`, one can now truly test this behaviour with the 25th
blog.
Second, the same example in Pages Router docs includes:
> return { paths, fallback: false }
In this case, again, this part below:
> If /blog/26 is requested, Next.js will generate and cache this page
on-demand
is incorrect. When setting `fallback` to `false`, the page is never
generated on-demand and returns 404 instead as there is no 26th blog
post in the fetched data. So the fix changes the value of `fallback` to
`blocking`, to mirror the App Router's `dynamicParams` value in the
guide. This makes is more consistent and, more importantly, reproducible
example.
**clarifying the on-demand section:**
The sections dedicated to **on-demand revalidation** do not currently
mention that revalidation works differently from the time-based one. One
may assume the first request after on-demand revalidation returns stale
data (just like time-based).
But that's not true, the next request after on-demand revalidation (with
Server Actions for example) generates the content on-the-fly and returns
fresh data right away. It wasn't clear to me so I tested it myself and
was surprised (and happy) that it is this smart. I think it's very
important to clarify this distinction in the guide.
-----
I hope this makes sense. I'm quite responsive these days and will change
it based on your feedback (if any). Thanks!
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Co-authored-by: Joseph <joseph.chamochumbi@vercel.com>
