Three npm forks of one React component were the best bug report it ever got

The fork did not describe a problem, it published the call signature it wanted. Its example passed `currentPage`, `isExpansion`, `onTryMoveNextPage` and `onChangedCurrentPage` ^[8]. The upstream component accepted `initialCurrentPage`, `initialIsExpansion` and `onChangeCurrentPage` ^[9]. That prefix is the whole disagreement, and the maintainer says as much: `initial` means the component takes a starting page and then never lets the caller touch it again ^[20][10].

Ownership decides what the host app can build. A parent that cannot set the page cannot jump to it from a table of contents or keep it in the URL, and it cannot refuse the move when the next chapter has to be bought first ^[11].

The retrofit has two traps worth copying. The `onChange` call belongs inside the setter, not in an effect watching the value, because in controlled mode the local value never changes, so the effect never fires and the parent hears nothing ^[13]. The setter also needs the current value and the current callback held in refs, or every render hands out a new setter and everything downstream re-renders with it ^[12].

The harder question is what happens to state the component writes for itself. Going fullscreen forces the expanded view and restores the previous value on exit; switching to a two-page spread rounds the current page down to an even number ^[14]. Under controlled props neither can simply happen. The resolution is the one a controlled text input already uses: the component asks through `onChange`, and if the parent ignores it, nothing moves ^[15].

Read as a report, the fork's commit log arrives pre-triaged. Of four visible changes, two match fixes the maintainer made anyway, one of them about a year later ^[6][7][19]. The remaining one, the controlled example, is the item he did not get to for four years ^[7]. The arithmetic is unkind. The oldest fork appeared about three months after first publication and ran for nearly a year ^[4], so `controlled.tsx` existed no later than fifteen months in, leaving a minimum of thirty-three months between a working sketch of the API and 1.1.0 shipping it ^[18].

None of this required the fork authors to cooperate, and they did not: no issue, no pull request ^[3]. It required only that the fork be findable, which it was, since it carried the upstream description and repository URL under a near-identical name and turned up while the maintainer was browsing npm ^[2], and that it be alive, which its version number showed at 0.6.3 against upstream's 0.3.5 ^[5]. Version 1.1.0 now takes `currentPage` and `isExpansion` as optional independent props ^[16] and adds `onTryMoveNextPage` and `onTryMovePrevPage`, which fire before the page changes ^[17]. That last pair is the paywall hook, and its name came from someone who never said a word ^[8].