eslint complains about no-unnecessary-type-assertion when typing a dictionary-type state variable

[tvogel]

Hi!

I am using a pinia store with a state variable that is supposed to store a dictionary, initially empty. The definition is like this:

    contourContainers: {} as Record<string, ContourContainer>,

Since upgrading my eslint configuration (using antfu now), it complains about

This assertion is unnecessary since the receiver accepts the original type of the expression.eslint[ts/no-unnecessary-type-assertion](https://typescript-eslint.io/rules/no-unnecessary-type-assertion)

but I need the assertion because otherwise, pinia will not know and forward the correct type.

Am I missing the proper way to handle this?

[sueun-dev]

The rule is only checking assignability there, not inference. {} is assignable to the state's receiver type, so it flags the as Record<...> as redundant. It isn't redundant for inference though: drop the assertion and pinia infers contourContainers as {}, so indexing it then errors with TS7053 ('key' can't be used to index type '{}').

Cleanest fix that keeps both eslint and the type happy is to type the whole state() return instead of casting inline:

interface State {
  contourContainers: Record<string, ContourContainer>
}

state: (): State => ({ contourContainers: {} }),

No assertion, so no-unnecessary-type-assertion stays quiet and the Record type still flows through. That's the interface pattern the pinia state docs suggest as the alternative to inline casts.

[posva]

You can disable the rule, it doesn’t seem to fit your usage. It might be worth considering doing

contourContainers: {} as Record<string, ContourContainer | undefined>,