Support for Intl.supportedValuesOf?

[kyllerss]

Perhaps I'm looking in the wrong place, but in VSCode (using the Svelte extension - v108.1.0) I'm getting a warning when I use Intl.supportedValuesOf stating that supportedValuesOf it is not part of Intl.

This feature is fully supported by all major browsers.

I made sure to set VSCode's Typescript support to ESNext, but that doesn't seem to make any difference. A similar issue was reported to VSCode's team, but they said it was the responsibility of the extension owner.

I so I guess my question is, has anyone run into this issue and is the right place to fix this at the Svelte VSCode extension? Any tips on how to make the warning go away?

[harshagarwalnyu]

This is a TypeScript lib configuration issue, not a Svelte-specific bug. Intl.supportedValuesOf was added in ES2021, specifically in the ES2021.Intl library. The Svelte VSCode extension uses your project's tsconfig.json, not VSCode's TypeScript settings — so changing VSCode's TS version has no effect.

Fix: add ES2021.Intl (or later) to your tsconfig lib array:

{
  "compilerOptions": {
    "lib": ["ES2021", "ES2021.Intl", "DOM", "DOM.Iterable"]
  }
}

Or use a superset that includes it:

{
  "compilerOptions": {
    "lib": ["ES2022", "DOM", "DOM.Iterable"]
  }
}

Why it's confusing: SvelteKit's default tsconfig.json (generated by create-svelte) historically extends @tsconfig/svelte which targets ES2017. Upgrading target alone isn't enough — target controls output syntax, lib controls what type definitions are available. You need the lib update.

Verify after changing: restart the Svelte Language Server (Ctrl+Shift+P → "Svelte: Restart Language Server") and the Intl.supportedValuesOf error should disappear.