TypeStript 入门 - 09：unknown #

let un: unknown;

//1.任何类型的值都可以赋值给unknown
un = 'pt';
un = 11;

let un: unknown;
un = 'pt';
un = 11;

let an: any;
an = 123;
an = "123";

//! 2.unknown 与any 可以互相赋值
un = an;
an = un;

let un: unknown;
un = 'pt';
un = 11;

//! 3.unknown变量，不可以访问变量的任何属性和方法, 也不能作为函数、类来使用
//un.a; 报错
//un(); 报错
//new unknow(); 报错

//! 4.任何类型与unknown联合， 得到的unknown类型
type UnionUnknown = unknown | null | string | number
//type UnionUnknown = unknown

//! 5. 任何类型与unknown交叉,unknown 被忽略，得到的是与它交叉的类型
type inter = unknown & null
//type inter = null

//! never 是unknown 的子类型
type isNever = never extends unknown ? true : false
//type isNever = true

//! keyof unknown 是never
type key = keyof unknown;
//type key = never

//! unknown类型遍历无用
type IMap<T> = {
	[P in keyof T]: number
}
type T = IMap<unknown>;
//type t = {}
let t: T = { name: "pt" };

let k: unknown = 1;
let n: Number = 1;
//! unknown类型不能和number类型进行 +运算, 但是可以用于等于与不等于操作
// console.log(k + n); 报错

console.log(k === n);//true
console.log(k !== n);//false