Typescript Cartesian Product

cartesianProduct.ts

const f = (a: any[], b: any[]): any[] =>
    [].concat(...a.map(a2 => b.map(b2 => [].concat(a2, b2))));

export const cartesianProduct = (a: any[], b: any[], ...c: any[]) => {    
    if (!b || b.length === 0) {
        return a;
    }
    const [b2, ...c2] = c;
    const fab = f(a, b);
    return cartesianProduct(fab, b2, c2);
};

Tell me that you cannot solve the problem of the cartesian product in TypeScript without telling me that you cannot solve the problem of the cartesian product in TypeScript.

Which is fine, by the way. I don't know the solution either. I came here looking for the solution and make the note that the proposed solution is wrong, in the sense explained in the comment above. Nothing else.

If you find the right solution, I'd be glad if you posted it here.

Mixed types are tricky.
Give this a try.

The key is [...T]

export const cartesianProduct = <T extends any[][]>(a: [...T]): Array<{[K in keyof T]: T[K][number]}> => a.reduce((a, b) => a.flatMap(d => b.map(e => [d, e].flat())))