use Partial in nested property with typescript

Question

Say I have a type like this;

interface State {
  one: string,
  two: {
    three: {
      four: string
    },
    five: string
  }
}

I make

Answer 1

For TypeScript 2.8 or later, the following type should fix problem about Array property.

type NestedPartial = {
    [K in keyof T]?: T[K] extends Array ? Array> : NestedPartial
};

Please see the example below.

interface Foo {
    NumProp: number;
    SubItem: Foo;
    SubItemArray: Foo[];
}

Valid Result with conditional type

Invalid Result

https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-8.html