如何从打字稿中带标签的联合类型中提取类型? [英] How to extract a type from a tagged union type in typescript?

问题描述

说已经定义了一个类型:

Say there is already a type defined as this:

export type Item = {
  type: 'text',
  content: string
} | {
  type: 'link',
  url: string
}

是否可以从类型Item中提取link部分?我的意思是，是否可以定义类型ExtractTypeFrom:

Is it possible to extract the link part from the type Item? I mean, is it possible to define a type ExtractTypeFrom:

type LinkItem = ExtractType<Item, 'type', 'link'>

LinkItem将是:

{
  type: 'link',
  url: string
}

推荐答案

是的，您可能非常亲密，可以使用预定义的Extract条件类型.您可能需要传入一个类型作为第二个参数，该类型可以是您要寻找的类型的基本类型:

Yes it is possible you are very close, you can use the predefined Extract conditional type. You can will need to pass in, as the second argument, a type that can be a base type for the type you are seeking:

type LinkItem = Extract<Item, { type: 'link' }> // will be  { type: "link"; url: string; }

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