TypeScript 特殊类型处理
Smoothness 2023/6/20 TypeScript
本文介绍TypeScript中一些特殊类型的判断。
#
TypeScript中类型的判断要根据它的特性来。
# IsAny
- any 类型与任何类型的交叉都是 any，也就是 1 & any 结果是 any。
type IsAny<T> = 'string' extends ('string' & T) ? true : false type typeAny = any type anyResult = IsAny<typeAny>1
2
3
# IsEqual
- 这种写法可以避免
any的问题，具体原理等后面原理讲解。type IsEqual<A, B> = (<T>() => T extends A ? 1 : 2) extends (<T>() => T extends B ? 1 : 2) ? true : false type typeEqual1 = 1 type typeEqual2 = 2 type equalResult = IsEqual<typeEqual1, typeEqual2>1
2
3
4
# IsNever
- never 在条件类型中也比较特殊，如果条件类型左边是类型参数，并且传入的是 never，那么直接返回 never。
type IsNever<T> = [T] extends [never] ? true : false type typeNaver = never type naverResult = IsNever<typeNaver>1
2
3
# GetOptional
- 可选索引的值为 undefined 和值类型的联合类型。
type people = { name: string, age: number, love?: string } type GetOptional<Obj extends Record<string, any>> = { [ Key in keyof Obj as {} extends Pick<Obj, Key> ? Key : never ]: Obj[Key] } type opPeopleResult = GetOptional<people>1
2
3
4
5
6
7
8
9
10
11
12
13
# GetRequired
- 反着取一下就可以。
type people = { name: string, age: number, love?: string } type GetRequired<Obj extends Record<string, any>> = { [ Key in keyof Obj as {} extends Pick<Obj, Key> ? never : Key ]: Obj[Key] } type rePeopleResult = GetRequired<people>1
2
3
4
5
6
7
8
9
10
11
12
13
# GetSpecifiedAttribute
- 合并上面两个写法
type GetSpecifiedAttribute<Obj extends Record<string, any>, S = 'Options' | 'Required'> = { [ Key in keyof Obj as {} extends Pick<Obj, Key> ? (S extends 'Optional' ? Key : never) : (S extends 'Required' ? Key : never) ]: Obj[Key] } type getAttrType = GetSpecifiedAttribute<people, 'Optional'>1
2
3
4
5
6
7
8
9
10
# as const
- TypeScript 默认推导出来的类型并不是字面量类型。但是类型编程很多时候是需要推导出字面量类型的，这时候就需要用 as const：
```TypeScript
const zs = {
name: 'zs',
age: 12
}
const ls = {
name: 'ls',
age: 19
} as const
type zsType = typeof zs
type lsType = typeof ls
```