DeepObjectPartial<T>: Deep Partial, but Only Objects are Optional

deep-object-partial.ts

type ExampleType = {
	a: string
	b: {
		x: string
		y: number
	}
	c: string[]
}

type ExtractOptionalKeys<TYPE> = { [KEY in keyof TYPE]: TYPE[KEY] extends Record<string, any> ? (TYPE[KEY] extends Array<any> ? never : KEY) : never }[keyof TYPE]

type DeepObjectPartial<TYPE extends Record<string, any>> = {
	[KEY in ExtractOptionalKeys<TYPE>]?: DeepObjectPartial<TYPE[KEY]>
} & Omit<TYPE, ExtractOptionalKeys<TYPE>>

export const a: DeepObjectPartial<ExampleType> = {
	a: 'wow',
	c: ['a']
}

export const b: DeepObjectPartial<ExampleType> = {
	a: 'wow',
    b: {
        x: 'wow',
        y: 1
    },
	c: []
}

Can be tested on TypeScript Playground

Designed to work in TS 4.3.5 and 4.5.2