I would like to create type from `key` in my code:

```
const arr = [{ key: "a", nnumber: 11 }, { key: "b", nnumber: 1 }];

function test<Keys['key'] extends keyof string>(keys: Keys): Keys[] {
    return arr.map((item) => item.key);
}

// should return "a", "b"
const tmp = test(arr);
//   ^?

```

Can anyone help me to create type for return ["a", "b"].

Thank you