[英]Typescript ReturnType issue
Im trying to get the correct return type based on the method key of an interface.我试图根据接口的方法键获取正确的返回类型。 Typescript is showing an issue here but i cant work out why.
Typescript 在这里显示了一个问题,但我不知道为什么。
interface Provider {
reboot?(a: string): (string | null)[]
cc?(): Promise<string>
}
type ProviderReturn<K extends keyof Provider> = ReturnType<Provider[K]>
Your interface defines an object with 2 potentially undefined methods.您的接口定义了一个 object 和 2 个可能未定义的方法。
ReturnType
does not work on undefined
ReturnType
不适用于undefined
You can do follwing with Nonnullable
您可以使用
Nonnullable
进行后续操作
interface Provider {
reboot?(a: string): (string | null)[]
cc?(): Promise<string>
}
type ProviderReturn<K extends keyof Provider> = ReturnType<NonNullable<Provider[K]>>
If the optional part matters, you can use a conditional type:如果可选部分很重要,您可以使用条件类型:
interface Provider {
reboot?(a: string): (string | null)[]
cc?(): Promise<string>
foo(): string
}
type ProviderReturn<K extends keyof Provider> = undefined extends Provider[K] ? ReturnType<NonNullable<Provider[K]>> | undefined : ReturnType<NonNullable<Provider[K]>>
type a = ProviderReturn<'reboot'> // (string | null)[] | null;
type b = ProviderReturn<'foo'> // string
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