[Tanstack Start] Does HMR/Fast Refresh work?

[loukhin]

First of all, I'm not sure about the terminology here but what I'm referring to is the ability to save (cmd+S) route component file without the state and/or input value resetting

What I'm expecting:

1. bun --bun run dev
2. Go to localhost:3000
3. Click the button to update count state
4. Type something in the input
5. Save the file in the IDE
6. The count state and input value should not reset to 0 and empty respectively

What actually happens:

1. bun --bun run dev
2. Go to localhost:3000
3. Click the button to update count state
4. Type something in the input
5. Save the file in the IDE
6. The count state reset to 0 and the input became empty

Reproduction: https://github.com/loukhin/tss-hmr-fast-refresh-problem
(It's just a normal bunx @tanstack/cli@latest create with state and input added)

What I've tried and did not work:

• Disabling ssr both directly in the route and in start.ts

What I've tried and kinda work:

• Splitting export Route and function Component() code into separate file.
• Adding .lazy suffix. (localhost:3000/working in the reproduction code)

I don't know if both methods are the correct way to do it but it made my life a bit harder so I want to avoid it if I can.

[manimovassagh]

[schiller-manuel]

dont just paste some AI output here. this is not helpful

[schiller-manuel]

fixed this in https://github.com/TanStack/router/releases/tag/release-2026-03-21-0031

[schiller-manuel]

no idea about bun, sorry, i dont use it.

from your reproducer

in Nextjs, the code below doesn't re-render when you comment/uncomment 2 previous lines from the page

how do you determine that it re-renders?

[loukhin]

Sorry for the incomplete reproducer, I forgot to include the expecting behavior.

I determine with the animation (re-playing) and the DOM updates (I'm expecting only "Hello World" update, but in this screenshot of Chrome DevTools the sibling below are also updated)

But I also re-checked and the input also get reset if it's below the comment so you can also use that for the e2e test, I've updated the reproducer to add another input below the commented section.

[schiller-manuel]

i experience the same "input is lost" in nextjs https://github.com/schiller-manuel/nextjs-hmr-input-repro/blob/main/app/page.tsx

[loukhin]

and it's the one thing I didn't re-check in nextjs and didn't notice this behavior before 😅
sorry for wasting your time and appreciated the help!

[schiller-manuel]

no worries :)