typescript - 为什么可以索引类型为 never 的对象？

Question

在 tsconfig.json 中启用了 strict 后，为什么 tsc 在索引 never< 类型的对象时不会发出错误?

const mystery = ({ foo: 1 } as never)

console.log(mystery['foo'])  // no error
console.log(mystery.foo)  // Property 'foo' does not exist on type 'never'.

export {}

Playground example

Answer 1

It's bug #41021 :

'never' (and probably 'void') shouldn't be silently indexable types

DanielRosenwasser commented on Oct 10, 2020

let x = [1, 2, 3, 4].forEach(x => { console.log(x));
x["hello"] = 123;

Expected: an error that x is possibly void or somethingActual: no errors

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DanielRosenwasser commented on Oct 10, 2020

Actually, never seems to suffer from the same issue..

TypeScript 团队正在积极修复它，但尚无可用的修复方法。

Here's更简单的复制:

declare let mystery: never;

console.log(mystery["foo"]);    // No error
console.log(mystery.foo);       // Property 'foo' does not exist on type 'never'.