在 Typescript 中将类型定义为“来自枚举的所有可能性”

Question

I have the following enum

export enum USER_GROUPS {
  "Admin",
  "Design",
  "FrontEnd",
  "BackEnd"
}

And the following function

const isUserOfType = (userGroupId: number, userType: USER_GROUPS) => {
  return userGroupId === USER_GROUPS[userType];
};

Where

isUserOfType(2, "Design") // returns true
isUserOfType(1, "BackEnd") // returns false

The problem is the second param is not assignable to type: USER_GROUPS ... I could do the following

isUserOfType = (
    userGroupId: number,
    userType:
      | USER_GROUPS.Admin
      | USER_GROUPS.Design
      | USER_GROUPS.FrontEnd
      | USER_GROUPS.BackEnd
  ) => {
      return userGroupId === USER_GROUPS[userType];
    };

However, that is annoying to do on every function. and defining a completely separate type defeats some of the purpose of an enum

Answer 1

As mentioned, you can use keyof typeof to get all the Enum keys:

export enum USER_GROUPS {
  "Admin",
  "Design",
  "FrontEnd",
  "BackEnd"
}

type USER_GROUPS_KEYS = keyof typeof USER_GROUPS;

const isUserOfType = (userGroupId: number, userType: USER_GROUPS_KEYS) => {
  return userGroupId === USER_GROUPS[userType];
};

isUserOfType(2, "Design") // returns true
isUserOfType(1, "BackEnd") // returns false

Personally I would use string enums or a string union type instead:

export enum USER_GROUPS_V2 {
  "Admin" = "Admin",
}

export type USER_GROUPS_UNION_TYPE = 
  | "Admin"
  | "Design";

but if you're stuck with another data source that requires these to be numerical, then the above will work.