TypeScript: wrapping an optional value inside a store makes it non-optional

[kevinrenskers]

Describe the bug

When I wrap an optional value in a writable store, it becomes non-optional.

Reproduction

These 2 lines are all you need:

let value: string | undefined;
let store = writable(value);

The type of store is Writable<string>.

I can work around it by manually specifying the type:

let store = writable<string | undefined>(value);

But it's weird that this is necessary.

Logs

No response

System Info

System:
    OS: macOS 14.5
    CPU: (10) arm64 Apple M1 Max
    Memory: 48.22 MB / 32.00 GB
    Shell: 3.7.1 - /opt/homebrew/bin/fish
  Binaries:
    Node: 18.17.1 - ~/Library/pnpm/node
    npm: 9.6.7 - ~/Library/pnpm/npm
    pnpm: 8.15.3 - ~/Library/pnpm/pnpm
  Browsers:
    Safari: 17.5
  npmPackages:
    svelte: ^4.2.18 => 4.2.18

Severity

annoyance