OptionalUndefined
题目
Implement the util type OptionalUndefined<T, Props>
that turns all the properties of T
that can be undefined
, into optional properties. In addition, a second -optional- generic Props
can be passed to restrict the properties that can be altered.
ts
OptionalUndefined<{ value: string | undefined; description: string }>;
// { value?: string | undefined; description: string }
OptionalUndefined<
{
value: string | undefined;
description: string | undefined;
author: string | undefined;
},
"description" | "author"
>;
// { value: string | undefined; description?: string | undefined, author?: string | undefined }
解答
ts
type Merge<T> = {
[K in keyof T]: T[K];
};
type OptionalUndefined<
T,
Props extends keyof T = keyof T,
OptionsProps extends keyof T = Props extends keyof T
? undefined extends T[Props]
? Props
: never
: never
> = Merge<
{
[K in OptionsProps]?: T[K];
} & {
[K in Exclude<keyof T, OptionsProps>]: T[K];
}
>;