如何在 TypeScript 中创建一个 Record<>（或其他映射）键控到一个枚举作为联合

Question

我需要创建键控到枚举的函数映射，但如果我使用 Record<> 实用程序类型，它似乎需要 all 枚举值存在于映射对象。我需要它们都是可选的。例如：

enum ContentType {
  Text,
  Image,
  Video,
}
type MapFn = (value: string) => string;

type ContentTypeMap = Record<ContentType, MapFn>;

const myMap = {
  [ContentType.Text] : (value:string) => (value.toUpperCase),
} as ContentTypeMap;

结果：

Conversion of type '{ 0: (value: string) => () => string; }' to type 'ContentTypeMap' may be a mistake because neither type sufficiently overlaps with the other. If this was intentional, convert the expression to 'unknown' first.
  Type '{ 0: (value: string) => () => string; }' is missing the following properties from type 'ContentTypeMap': 1, 2

我也简单试过：

type ContentMap = { [ContentType]: MapFn };

但是编译器抱怨使用 ContentType:

A computed property name in a type literal must refer to an expression whose type is a literal type or a 'unique symbol' type.

我认为枚举算作文字，但我想在这种情况下不是？

我可以使用什么来创建对象不需要实现所有枚举值的 (enum) => (function) 映射？

Answer 1

I also tried simply:
type ContentMap = { [ContentType]: MapFn };

你很接近，但它需要是这样的：

type ContentMap = { [key in ContentType]: MapFn };

然后将它们设为可选：

type ContentMap = { [key in ContentType]?: MapFn };

Playground link

如果您更喜欢使用 Record 表示法，则可以使用实用程序类型 Partial 使其所有属性都可选：

type ContentMap = Partial<Record<ContentType, MapFn>>;

Playground Link

如何在 TypeScript 中创建一个 Record<>（或其他映射）键控到一个枚举作为联合

How to create a Record<> (or other mapping) in TypeScript keyed to an enum as a union

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