If you’ve worked on more than one code migration, you already know the punchline: none of them are the same.  

Sure, it sounds like a React 17 → 18 upgrade should follow the same plan for everyone.   

But a real-world code migration always find a way to be uniquely painful. Your app uses different corners of the library.  

Your plugin stack has its own fingerprint.  

Your engineers wrote some “just for now” code that’s still running five years later.  

Whatever you thought the code migration would be, it won’t be.  

This was one of the biggest takeaways in a recent episode of Tern Stories, where we looked inward for once.  

My cofounder Ryan and I talked through what we’ve seen in our own migrations and the ones we’ve supported across companies.  

Despite the variety, a few consistent truths emerged.

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