TypeScript 中有没有办法直接从 object 的键创建新类型？

Question

Is there a way in TypeScript to create a new type directly from the keys of an object? In the following example TypeScript correctly complains ( 'msg' refers to a value, but is being used as a type here. ) about msg referring to a value but I was wondering if there is a way to get this working without having to create a separate type definition?

const msg = {okay: 'Okay', cancel: 'Cancel'};

function getMsg(id: keyof msg): string {
   return msg[id];
}

Answer 1

typeof gets a type from a value. Then you put keyof in front of that to get this slightly odd looking type:

const msg = {okay: 'Okay', cancel: 'Cancel'};

function getMsg(id: keyof typeof msg): string {
   return msg[id];
}

Playground