Romaji to Kana Converter: React & Next.js — Chapter 8, Exercise 2
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TASK
This chapter's own real test showed that GET / returns a genuine 404
once basePath is set to /romaji. A teammate is confused, since the
app clearly still works -- just under a different path. Explain,
precisely, what "the app's own root" actually means once basePath is
configured, and why 404 is the honest, correct response rather than a
bug.

SOLUTION

Before basePath is set, "the app's own root" and "the literal URL
path /" happen to be the exact same thing, which makes it easy to
accidentally think of them as inherently the same concept rather than
two things that just happened to coincide. Setting
basePath: '/romaji' doesn't add a second copy of the app at a new
location while leaving the original one at / -- it genuinely moves
where the app's own root actually is. After that change, the app's
own root IS /romaji; the literal path / was never a special,
permanently-reserved address for "wherever the app lives," it was
just wherever the app happened to be mounted before this specific
configuration changed.

This chapter's own real test makes that concrete: GET /romaji returns
a genuine 200 with the real homepage content, while GET / returns a
genuine 404 -- not because something broke, but because there
genuinely is no route registered at / anymore. The app was never
listening in two places at once; it moved. Requesting the address it
used to live at, now that it doesn't anymore, is structurally
identical to requesting any other real, honestly nonexistent path --
a 404 is the correct, accurate answer, not a symptom of something
going wrong.

The real reason this feels surprising is that most day-to-day web
development happens with basePath unset, where "the root" and "/"
are permanently fused together by default, making it easy to
internalize / as meaning "the app" specifically rather than
"wherever the app currently happens to be mounted." basePath exposes
that those were always two separate facts that merely lined up by
default -- and once they're deliberately un-lined-up, a 404 at the
old address is exactly what a correctly working, successfully moved
app should honestly report.

WHY THIS WORKS AS AN ANSWER
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It distinguishes "the app's own root" (a relative concept, wherever
it's currently mounted) from the literal path "/" (one specific
possible value for that concept), and explains that basePath
genuinely relocates the former rather than duplicating the app at a
new address -- making the 404 at the old address the honest, correct
outcome rather than a fault.