Typescript：如何命名可能未定义的字符串数组？

Question

I'm using Typescript in my React Native app and I define the following array:

const arr: string[] = Platform.select({
  ios: ["a", "b", "c"],
  android: ["a", "b", "c"]
})

VsCode underlines arr and tells me Type 'string[] | undefined' is not assignable to type 'string[]' Type 'string[] | undefined' is not assignable to type 'string[]' , so I changed it to

const arr: string[] | undefined = Platform.select({
  ios: ["a", "b", "c"],
  android: ["a", "b", "c"]
})

VsCode removes the underline on arr in the definition, but when I use it in my code it underlines it there and says Argument of type 'string[] | undefined' is not assignable to parameter of type 'string[]' Argument of type 'string[] | undefined' is not assignable to parameter of type 'string[]'

I think the problem is that Platform.select() might return undefined , but then I'm using arr in my code for operations that require it to have type string[] instead of string[] . How can I modify my code to remove all these warnings?

Answer 1

You can give an empty array as the default value when Platform.select returns undefined using nullish coalescing operator .

This would also work

const arr: string[] = Platform.select({
  ios: ["a", "b", "c"],
  android: ["a", "b", "c"]
}) ?? []

Answer 2

This may suffice:

const arr: string[] = Platform.select({
  ios: ["a", "b", "c"],
  android: ["a", "b", "c"]
}) as unknown as string[]

But, I would be cautious. It's usually better to listen to Typescript and adjust your design accordingly.