useEffect fired twice, on mount, every single time, in development only. The API call inside it — a POST that created a resource — ran twice, and for about a day we had duplicate records showing up in a table that should have had exactly one insert per page load. The first reaction, and why it ...
Source: [Dev.to](https://dev.to/rbonweb/useeffect-fired-twice-and-it-found-a-real-bug-5438)