typescript索引查询类型

type Props = {a: number, b: string, c:boolean}


type TypeA = Props['a'] //number
let a: TypeA = 1

type TypeB = Props['a' | 'b']  //number | string
let b: TypeB = '1'

type TypeC = Props[keyof Props] //number | string | boolean
let c: TypeC = '1'