断言

基本语法

TypeScript 的类型断言要遵守一条**「互信」规则**

源类型与目标类型之间至少要有**重叠（互相兼容）**的部分，否则编译器会报错。

as known

在很多场景下直接 as T 会被编译器拒绝，而先 as unknown 再 as T 可以分两步拆掉编译器的防线。

const s = "abc";
const n = s as number;     // ❌ 报错：两者没有重叠，编译器不信

const s = "abc";
const n = s as known as number;