Romaji to Kana Converter: React & Next.js — Chapter 8, Exercise 1
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TASK
Chapter 5 also built a client-side box that calls convert() directly,
with no fetch() call at all. Explain, using this chapter's own real
findings, why that box needs no basePath fix whatsoever, while the
server-comparison box's own fetch call does.

SOLUTION

The real basePath gotcha this chapter demonstrated is specifically
about URLs -- a string like "/api/convert" that has to correctly
resolve to wherever the app is actually mounted, whether that's the
real web root or a real subpath like /romaji/. The problem only
exists at all because a fetch() call has to know, and get right, an
actual network address to send a request to.

The client-side box has no such string anywhere in it. Its own
onChange handler calls convert(input) directly -- a plain, synchronous
JavaScript function call inside the same already-loaded React
component. There's no URL involved at any point: no request is
constructed, no path is resolved, nothing is sent over the network at
all. convert() doesn't live "at" a path the way /api/convert does; it
lives wherever the component's own already-loaded JavaScript happens
to be, which is already correct by construction the instant the page
itself has loaded successfully.

Put differently, basePath's own real job -- and the real reason a raw
fetch() call can get it wrong -- is rewriting where a browser looks
for something. A function call was never "looked for" anywhere; it's
just called, on an object reference the component already holds. That
category of gotcha structurally cannot apply to code that never
builds a URL string in the first place, which is exactly why the
client-side box needed zero changes anywhere in this chapter, while
the server-comparison box's own one hardcoded "/api/convert" string
was the one real line that had to change.

WHY THIS WORKS AS AN ANSWER
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It correctly identifies that the basePath gotcha is fundamentally a
URL-resolution problem, and that convert() called directly involves
no URL at any point -- a plain function call has nothing for basePath
to get wrong, which is why only the fetch-based box needed a real fix.