如何在解构语法中使用断言？

Question

In Typescript, how can I use assertion in destructuring?

type StringOrNumber = string | number

const obj = {
  foo: 123 as StringOrNumber
}

const { foo } = obj

I didn't find a convenient way to add number type assertion on const foo . Two workarounds are:

// A:
const { foo } = obj as { foo: number }

// B:
const { foo: foo2 } = obj

const foo = <number>foo2

The first is a burden to rewrite the obj 's type when its type is nested and complicated. The second seems weird. I'm assuming such a syntax like:

const { <number>foo } = obj

can absolutely help us asserting the type from nested and complicated destructuring.

Answer 1

According to the documentation , there is no way for casting the type right when destructuring. Apparently, there are no workarounds other than those that you provided.

Answer 2

I believe there are no possible way to do type assertion in destructuring objects or arrays.

But here are an alternative you can try.

const { foo, bar } = data;
const baz = foo as string;

// You can use string methods here.
console.log(baz.split(" "));