Type Alias UndefinedOnPartialDeep<T>

UndefinedOnPartialDeep: T extends BuiltIns
| Function
    ? T
    : T extends readonly unknown[]
        ? UndefinedOnPartialList<T>
        : T extends Map<infer K, infer V>
            ? Map<K, UndefinedOnPartialDeep<V>>
            : T extends ReadonlyMap<infer K, infer V>
                ? ReadonlyMap<K, UndefinedOnPartialDeep<V>>
                : T extends Set<infer K>
                    ? Set<UndefinedOnPartialDeep<K>>
                    : T extends ReadonlySet<infer K>
                        ? ReadonlySet<UndefinedOnPartialDeep<K>>
                        : T extends Record<any, any>
                            ? {
                                [KeyType in keyof T]: undefined extends T[KeyType]
                                    ? UndefinedOnPartialDeep<(...)>
                                    | undefined
                                    : UndefinedOnPartialDeep<(...)[(...)]>
                            }
                            : T

Create a deep version of another type where all optional keys are set to also accept undefined.

Note: This is only needed when the exactOptionalPropertyTypes TSConfig setting is enabled.

Use-cases:

When exactOptionalPropertyTypes is enabled, an object like {a: undefined} is not assignable to the type {a?: number}. You can use UndefinedOnPartialDeep<{a?: number}> to make it assignable.

Type Parameters

Example

import type {UndefinedOnPartialDeep} from 'type-fest';

type Settings = {
	optionA: string;
	optionB?: number;
	subOption: {
		subOptionA: boolean;
		subOptionB?: boolean;
	};
};

const testSettingsA: Settings = {
	optionA: 'foo',
	optionB: undefined, // TypeScript error if `exactOptionalPropertyTypes` is true.
	// @ts-expect-error
	subOption: {
		subOptionA: true,
		subOptionB: undefined, // TypeScript error if `exactOptionalPropertyTypes` is true
	},
};

const testSettingsB: UndefinedOnPartialDeep<Settings> = {
	optionA: 'foo',
	optionB: undefined, // `optionB` can be set to `undefined` now.
	subOption: {
		subOptionA: true,
		subOptionB: undefined, // `subOptionB` can be set to `undefined` now.
	},
};