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外观

IsFixedStringLiteralType

约 369 字大约 1 分钟

2026-02-11

题目

Sometimes you may want to determine whether a string literal is a definite type. For example, when you want to check whether the type specified as a class identifier is a fixed string literal type.

type Action<ID extends string> = { readonly id: ID };

Since it must be fixed, the following types must be determined as false.

  • never type
  • Union of string literal types
  • Template literal types with embedded string, number, bigint, boolean

Determine whether the given type S is a definite string literal type.

解题思路

待补充

答案

type IsFixedStringLiteralType<S extends string> = any

验证

import type { Equal, Expect } from '@type-challenges/utils'

type testcase =
  | Expect<Equal<IsFixedStringLiteralType<'ABC'>, true>>
  | Expect<Equal<IsFixedStringLiteralType<string>, false>>
  | Expect<Equal<IsFixedStringLiteralType<'ABC' | 'DEF'>, false>>
  | Expect<Equal<IsFixedStringLiteralType<never>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`${string}`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`${string & {}}`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`${number}`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`${bigint}`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`${boolean}`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`${true}`>, true>>
  | Expect<Equal<IsFixedStringLiteralType<`${false}`>, true>>
  | Expect<Equal<IsFixedStringLiteralType<`${null}`>, true>>
  | Expect<Equal<IsFixedStringLiteralType<`${undefined}`>, true>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${string}`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${string & {}}`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${number}`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${bigint}`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${boolean}`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${true}`>, true>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${false}`>, true>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${null}`>, true>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${undefined}`>, true>>
  | Expect<Equal<IsFixedStringLiteralType<`${string}DEF`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`${string & {}}DEF`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`${number}DEF`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`${bigint}DEF`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`${boolean}DEF`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`${true}DEF`>, true>>
  | Expect<Equal<IsFixedStringLiteralType<`${false}DEF`>, true>>
  | Expect<Equal<IsFixedStringLiteralType<`${null}DEF`>, true>>
  | Expect<Equal<IsFixedStringLiteralType<`${undefined}DEF`>, true>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${string}DEF`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${string & {}}DEF`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${number}DEF`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${bigint}DEF`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${boolean}DEF`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${true}DEF`>, true>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${false}DEF`>, true>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${null}DEF`>, true>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${undefined}DEF`>, true>>
  | true

参考

无