Type Alias OptionalKeysOf<BaseType>

OptionalKeysOf: Exclude<
    {
        [Key in keyof BaseType]: BaseType extends Record<Key, BaseType[Key]>
            ? never
            : Key
    }[keyof BaseType],
    undefined,
>

Extract all optional keys from the given type.

This is useful when you want to create a new type that contains different type values for the optional keys only.

Type Parameters

  • BaseType extends object

Example

import type {OptionalKeysOf, Except} from 'type-fest';

interface User {
	name: string;
	surname: string;

	luckyNumber?: number;
}

const REMOVE_FIELD = Symbol('remove field symbol');
type UpdateOperation<Entity extends object> = Except<Partial<Entity>, OptionalKeysOf<Entity>> & {
	[Key in OptionalKeysOf<Entity>]?: Entity[Key] | typeof REMOVE_FIELD;
};

const update1: UpdateOperation<User> = {
	name: 'Alice'
};

const update2: UpdateOperation<User> = {
	name: 'Bob',
	luckyNumber: REMOVE_FIELD
};

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