So basically this is a frustration kind of post. The title said it all.

What supposed to be something that's only several minutes had turned into several hours of waste as there were a LOT of hidden dependencies and side effects after upgrading. So I'll just create a small blog post to summarize what happened.

From 14 to 15 using Next's `codemod` assist

What happened was there are a lot of changes happened which is a little bit unintuitive. Like, why the hell that all request params is a promise? But the good thing is, the codemod already took care of those so it was a pretty okay-ish experience.

And then as I tried to run the dev server and also building, there were some weird issues with the recent adoption of turbopack into Nextjs ecosystem. Basically they're ditching webpack in favor of their "monopoly" and although it worked at first, later on I discovered that I also need to set the build stage to use Turbopack, effectively changing the script to next build --turbopack. It's weird, I haven't verified the changes, but I just need the confirmation that it works and hope that nothing goes wrong later on. At least I finally solved the Invariant: Expected to replace all template variables, missing VAR_ORIGINAL_PATHNAME in template errors which said to be caused by webpack . So... Webpack is now unsupported? What a great move, Vercel. If anything, I am more interested in using rspack but I'll see if it's going to be more effective later on. But so far, turbopack doesn't give me any smile.

But guess what? There are new hidden errors!

Did you know that Next.js 15 now uses React 19 by default and weird shit happens with React 19?

Let's start with how JSX namespace is not defined anymore, effectively forcing you to use React.JSX instead. Is that good? Is that bad? I don't know. Some sources and discussions in the internet said to use "jsx": "react-jsx" in the tsconfig.json (since I'm using Typescript), but the reality is that this is something that relates to React 19 so you'll need to use React.JSX namespace. Why does it now live in React's namespace, I don't know man. I don't like the looks of it as well. Is it because of the React Compiler? I don't know as well. I'll need to check this out more after I got more free time.

Verdict: Bad experience

What I thought to be some of a good experience when upgrading turned to be unpleasant. It's now 3AM and I should've slept but here I am writing a rant about tech stacks I probably going to move from soon or later. I realized that I have been writing even more code and having page.tsx layout.tsx and many others has put my editor's tabs with even less information I can use to distinguish about which page/route I am currently working on.

Now if you'll excuse me, I'll try to cheer myself with a picture of my waifu.

Source: https://x.com/puroku057/status/1973667584693379262

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You'll need to know that I spent 4 hours for debugging Next.js after upgrading to 15 from 14