联合类型上不存在 Typescript 属性 [英] Typescript property does not exist on union type

问题描述

这是我遇到过几次的情况，看起来应该相当简单，但是我找不到不将类型设置为 any 的解决方案

This is a situation I have ran into a couple of times, it seems like it should be fairly straightforward, but I can't find a solution that doesn't set the type to any

一个函数将两个不同的对象之一作为参数，检查接收到的对象，并返回相应的字段.

A function takes one of two different objects as the argument, checks which object has been received, and returns the corresponding field.

这是问题的简化版本，但问题是这两个对象只能通过它们的属性(没有重叠)来区分，而我无法访问任何属性，因为它们不存在在另一种类型.

This is a simplified version of the problem, but the issue is that the two objects are only distinguishable by their properties(which have no overlap), and I can't access any of the properties, because they're not present on the other type.

type Obj1 = {
  message: string
}

type Obj2 = {
  text: string
}

const getText = (obj: Obj1 |obj2): string => {
  if (obj.message) {
    return obj.message
  }

  return obj.text
}

推荐答案

你必须缩小类型.您可以使用 in 运算符.

You have to narrow down the type. You can do so by using the in operator.

const getText = (obj: Obj1 | Obj2): string => {
  if ("message" in obj) {
    return obj.message
  }

  return obj.text
}

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