替代 any
每当想使用 any 时，都应先考虑 unknown，它是 any 类型对应的安全类型，即在对 unknown 类型的值执行大多数操作之前，我们必须进行某种形式的检查。
Unknown
unknown 类型可以接受任何类型。
let value: unknown
let v1: any
const v2: bigint = 100n
value = false // OK
value = 6 // OK
value = 'blue' // OK
value = [1, 2, 3] // OK
value = ['hello', 10] // OK
value = null // OK
value = undefined // OK
value = new Error('hi') // OK
value = { o: 'hello' } // OK
value = Symbol('hello') // OK
value = v1 // OK
value = v2 // OK
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
但 unknown 类型只能赋予 unknown 及 any 类型。
let value: unknown
const v1: any = value // OK
const v2: unknown = value // OK
const v3: boolean = value // ERROR
const v4: number = value // ERROR
const v5: bigint = value // ERROR
const v6: string = value // ERROR
const v7: any[] = value // ERROR
const v8: null = value // ERROR
const v9: undefined = value // ERROR
const v10: never = value // ERROR
1
2
3
4
5
6
7
8
9
10
11
12
2
3
4
5
6
7
8
9
10
11
12
Unions and Intersection Types
1. 联合类型
除了和 any 类型外都返回 unknown 类型。
type U1 = unknown | any // any
type U2 = unknown | number // unknown
type U3 = unknown | string // unknown
type U4 = unknown | any[] // unknown
type U5 = unknown | null // unknown
type U6 = unknown | undefined // unknown
type U7 = unknown | never // unknown
1
2
3
4
5
6
7
2
3
4
5
6
7
2. 交叉类型
type I1 = unknown & any // any
type I2 = unknown & number // number
type I3 = unknown & string // string
type I4 = unknown & any[] // any[]
type I5 = unknown & null // null
type I6 = unknown & undefined // undefined
type I7 = unknown & never // never
1
2
3
4
5
6
7
2
3
4
5
6
7