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@typescript/vfs is not Node.js 25 compatible (localStorage.getItem is not a function) #3449
Description
Issue: @typescript/vfs fails in Node.js 25 due to changes in Web Storage implementation. Node.js 25 enabled Web Storage by default, but the package assumes it's running in a browser environment and directly calls localStorage.getItem("DEBUG") without checking if localStorage is properly available. This causes a "localStorage.getItem is not a function" error when the Web Storage API is enabled but not fully implemented. The issue affects all packages that depend on @typescript/vfs, including twoslash, @shikijs/twoslash, fumadocs-twoslash, and fumadocs-mdx.
Here is an issue in fumadocs-mdx that is a direct result of this, failing dependent project's npm install due to a broken post-install script: fuma-nama/fumadocs#2456. To reproduce, simply create a Fumadocs project in Node.js 25 and observe the error. Alternatively:
Reproducible code
Environment:
Node.js 25.0.0
@typescript/vfs 1.6.1
Steps to reproduce:
- Install Node.js 25.0.0
- Create a new project with @typescript/vfs as a dependency
- Run any code that imports @typescript/vfs
You will see the error:
TypeError: localStorage.getItem is not a function
at Object. (/path/to/node_modules/@typescript/vfs/dist/vfs.cjs.development.js:25:64)
Activity
docs(ci): enable localStorage in Node.js 25 to avoid build error
docs(ci): enable localStorage in Node.js 25 to avoid build error (#329)
Renegade334 commentedon Oct 31, 2025
FYI, this behaviour will be changing in the next Node.js release (nodejs/node#60351).
jakebailey commentedon Oct 31, 2025
Enough that this fix won't work?
Renegade334 commentedon Oct 31, 2025
Should be fine – the behaviour will be for
localStorageto throw an accessor exception on failure (as opposed to returning an empty object as it does now), which is already accounted for in the initialisation ofhasLocalStorage. It's more a question of whether or not you'll want to keep the compatibility hack for the soon-to-disappear buggy behaviour once it's gone.jakebailey commentedon Oct 31, 2025
Ah, yeah I think we're fine to leave it.
docs(ci): enable localStorage in Node.js 25 to avoid build error (Fil…