Object.Flatten suggestion

[SrBrahma]

I couldn't find a Flatten type for Objects, for a case like the following:

type A = {
  a: { x: 0 };
  b: { y: 1 };
}

type WhatIWant = { x: 0; y: 1 }

Being the keys dynamic, number of children unknown etc. I wanted a general solution.

The following is a single level flattening solution:

type NonObjectKeysOf<T> = {
  [K in keyof T]: T[K] extends Array<any> ? K : T[K] extends Record<string, any> ? never : K
}[keyof T];

type ValuesOf<T> = T[keyof T];
type ObjectValuesOf<T extends Record<string, any>> = Exclude<
  Exclude<Extract<ValuesOf<T>, Record<string, any>>, never>,
  Array<any>
>;

type UnionToIntersection<U> = (U extends any
  ? (k: U) => void
  : never) extends ((k: infer I) => void)
  ? I
  : never;

type Flatten<T> = Pick<T, NonObjectKeysOf<T>> &
  UnionToIntersection<ObjectValuesOf<T>>;

I have replaced Object and object to Record<string, any> to shut eslint ts errors up.

I have no idea on why it works, but it does hehe. It was taken from here: https://flut1.medium.com/deep-flatten-typescript-types-with-finite-recursion-cb79233d93ca. The given link also shows up a multi level solution, for deeper object flattening.