(TypeScript) Why can't I setState with an object containing the keys of my state type

Why doesn’t this work:

export interface IState {
    username: string;
    password: string;
}

// ...

private onInputChange(e: Event, field: keyof IState) {
    const target = e.target as HTMLInputElement;
    this.setState({ [field]: target.value });
}

Am I incorrect in thinking this should work? field is by definition one of the keys of IState, so defining an object containing only field as keys should be a valid IState object. Is there an issue with the preact type declarations, or have I misunderstood something?

[pmkroeker]

This seems to be cause as it did not match Pick<State, keyof State>, so it was trying to match explicitly with State, when it should have been Partial<State>.

[pmkroeker]

Interesting. I think I played around with using Partial and it had some other side effects that I didn’t like, also, the React typings don’t use Partial for setState but Pick like ours do. Will investigate. Related typing in react