typescript 对象解构中的类型
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Types in object destructuring
提问by Estus Flask
This
这个
const { foo: IFoo[] } = bar;
and this
和这个
const { foo: Array<IFoo> } = bar;
will reasonably cause an error.
将合理地导致错误。
And this
和这个
const { foo: TFoo } = bar;
will just destructure TFooproperty.
只会破坏TFoo财产。
How can types be specified for destructured object properties?
如何为解构的对象属性指定类型？
回答by artem
It turns out it's possible to specify the type after :for the whole destructuring pattern:
事实证明，可以:在整个解构模式之后指定类型：
const {foo}: {foo: IFoo[]} = bar;
Which in reality is not any better than plain old
这实际上并不比普通的旧更好
const foo: IFoo[] = bar.foo;
回答by Stephen Paul
I'm clearly a bit late to the party, but:
我参加聚会显然有点晚了，但是：
interface User {
name: string;
age: number;
}
const obj: any = { name: 'Johnny', age: 25 };
const { name, age }: User = obj;
The types of properties nameand ageshould be correctly inferred to stringand numberrespectively.
该类型的属性name和age应正确推断string和number分别。
回答by Estus Flask
A follow-up to my own question.
对我自己问题的跟进。
Types don't need to be specified for object properties because they are inferred from destructured object.
不需要为对象属性指定类型，因为它们是从解构对象中推断出来的。
Considering that barwas typed properly, footype will be inferred:
考虑到bar输入正确，foo类型将被推断：
const bar = { foo: [fooValue], ... }; // bar type is { foo: IFoo[], ... }
...
const { foo } = bar; // foo type is IFoo[]
Even if barwasn't correctly typed (anyor unknown), its type can be asserted:
即使bar没有正确键入（any或unknown），也可以断言其类型：
const { foo } = bar as { foo: IFoo[] }; // foo type is IFoo[]
