Some ts utilities handy for well-typed reselect createSelector input functions.

selectArg.ts

/** Constructs a new function type from `F`, instead returning `R` */
export type Returns<F, R> = F extends (...args: any[]) => infer _
    ? (...args: Parameters<F>) => R
    : never;

/**
 * Given a (zero-indexed) positional argument number `n`
 * and a function call signature generic type `F`,
 * produce a well-typed function that selects that `n`th arg.
 * @example
 * const selectUser = selectArg<(state: Cache, user: User) => void>(1);
 */
export function selectArg<F extends (...args: any[]) => any>(
    n: 0
): Returns<F, Parameters<F>[0]>;
export function selectArg<F extends (...args: any[]) => any>(
    n: 1
): Returns<F, Parameters<F>[1]>;
export function selectArg<F extends (...args: any[]) => any>(
    n: 2
): Returns<F, Parameters<F>[2]>;
export function selectArg<F extends (...args: any[]) => any>(
    n: 3
): Returns<F, Parameters<F>[3]>;
export function selectArg<F extends (...args: any[]) => any>(
    n: 4
): Returns<F, Parameters<F>[4]>;
export function selectArg<F extends (...args: any[]) => any>(
    n: 5
): Returns<F, Parameters<F>[5]>;
export function selectArg<F extends (...args: any[]) => any>(
    n: 6
): Returns<F, Parameters<F>[6]>;
export function selectArg<F extends (...args: any[]) => any>(
    n: 7
): Returns<F, Parameters<F>[7]>;
export function selectArg<F extends (...args: any[]) => any>(
    n: 8
): Returns<F, Parameters<F>[8]>;
export function selectArg<F extends (...args: any[]) => any>(
    n: 9
): Returns<F, Parameters<F>[9]>;
export function selectArg<F extends (...args: any[]) => any, N extends number>(
    n: number
): Returns<F, Parameters<F>[N]> {
    return ((...args) => args[n]) as Returns<F, Parameters<F>[N]>;
}