Earlier quoted context omitted.
The problem is when--like in my case--people develop a project for a client and then go on with their lives, until the client notices a bug, or wants to implement a new feature months after. I tried to explain the client that I needed to upgrade the code before even being able to understand what the problem was, and I lost the client. As much as they suck, PHP apps from 10 years ago are still working great, and so ar…
Why do you need to upgrade the code to fix a bug or implement a new feature? I don't understand that. Keep React version and do what client wants.
Don't forget that a React project might be made of many libraries--not just React itself--that might be worse at supporting legacy versions and guaranteeing mooth upgrades.