LiteralUnion

Create a union type by combining primitive types and literal types without sacrificing auto-completion in IDEs for the literal type part of the union.

Currently, when a union type of a primitive type is combined with literal types, TypeScript loses all information about the combined literals. Thus, when such type is used in an IDE with autocompletion, no suggestions are made for the declared literals.

This type is a workaround for Microsoft/TypeScript#29729. It will be removed as soon as it's not needed anymore.

type LiteralUnion<LiteralType, BaseType extends Primitive> =
    | LiteralType
    | (BaseType & Record<never, never>);

type LiteralUnion<LiteralType, BaseType extends Primitive> =
    | LiteralType
    | (BaseType & Record<never, never>);

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

// Before

type Pet = 'dog' | 'cat' | string;

const petWithoutAutocomplete: Pet = '';
// Start typing in your TypeScript-enabled IDE.
// You **will not** get auto-completion for `dog` and `cat` literals.

// After

type Pet2 = LiteralUnion<'dog' | 'cat', string>;

const petWithAutoComplete: Pet2 = '';
// You **will** get auto-completion for `dog` and `cat` literals.

 Type

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

// Before

type Pet = 'dog' | 'cat' | string;

const petWithoutAutocomplete: Pet = '';
// Start typing in your TypeScript-enabled IDE.
// You **will not** get auto-completion for `dog` and `cat` literals.

// After

type Pet2 = LiteralUnion<'dog' | 'cat', string>;

const petWithAutoComplete: Pet2 = '';
// You **will** get auto-completion for `dog` and `cat` literals.

 Type

LiteralType

LiteralType

LiteralType

BaseType

BaseType extends Primitive

BaseType extends Primitive