Typescript泛型中的自定义枚举过于复杂

Question

if there is simpler way to write this down as this is extremely repetitive and just seems very wrong...

const FolderVisibility = new Enum<{
    PUBLIC: 'public',
    PRIVATE: 'private'
}>({
    PUBLIC: 'public',
    PRIVATE: 'private'
}) as Enum<{
    PUBLIC: 'public',
    PRIVATE: 'private'
}> & {
    PUBLIC: 'public',
    PRIVATE: 'private'
}

I want the IDE to be able to tell me that the FolderVisibility.PUBLIC == 'public' as the parameter is readonly anyway.

Here is Enum class, it has few of its own properties and one function

export default class Enum<T extends { [index: string]: string }> {
    private readonly map: T;
    public  readonly values: (T[keyof T])[];

    constructor(enums: T) {
        Object.defineProperty(this, 'map', { value: {} });

        for (let prop in enums) {
            if (enums.hasOwnProperty(prop)) {
                const value = enums[prop]
                if(typeof value != 'string'){
                    throw new EnumError(value)
                }
                this.map[prop] = value
                Object.defineProperty(this, prop, { value });
            }
        }

        Object.defineProperty(this, 'values', { value: Object.values(this.map) });
    }

    isValid(text: any) {
        if (!text) return true
        return this.values.includes(text)
    }
}

The point is, that if I copy the object used in constructor 4 times, it will even tell me that FolderVisibility.values is of type 'public' | 'private' 'public' | 'private'

PS: I have tried this, but it will give me string for FolderVisibility.values . also, it is still pretty long. const data = { PUBLIC: 'public', PRIVATE: 'private' }

const FolderVisibility = new Enum<typeof data>(data) as Enum<typeof data> & typeof data

Answer 1

The problem with object literals and literal types is that you can't get the compiler to infer a literal type for an object literal property. This is why specifying the generic type argument is necessary.

There is a part of your approach that can definitely be simplified, and that is the cast after the enum. Don't use a constructor, use a simple function as that has greater flexibility as to what it can return:

function Enum<T extends{ [P in keyof T]: string }>(enums: T) {

    let map : { [index: string]: string } = {}

    for (let prop in enums) {
        if (enums.hasOwnProperty(prop)) {
            const value = enums[prop]
            if(typeof value != 'string'){
                throw new EnumError(value)
            }
            map[prop] = value;
        }
    }
    let result = Object.assign({}, enums , {
        values: Object.values(map),
        isValid(text: string) {
            if (!text) return true
            return this.values.includes(text)
        }
    });
    // maybe frees the enum so no values are chanegd ?
    return Object.freeze(result);
}
const FolderVisibility = Enum<{
    PUBLIC: 'public',
    PRIVATE: 'private'
}>({
    PUBLIC: 'public',
    PRIVATE: 'private'
});
console.log(FolderVisibility.isValid("")) // Works
console.log(FolderVisibility.PRIVATE === "private" ) // And const fields of string literal type

We can also use the function above to augment an actual enum ,with less explicit typing needed:

enum FolderVisibilityProto {
    PUBLIC ='public',
    PRIVATE=  'private'
}
const FolderVisibility = Enum(FolderVisibilityProto);

Or we can change the Enun function a bit to take a callback that creates the enum internally so as not to ever have access to the non-augmented enum:

function Enum<T extends{ [P in keyof T]: string }>(enumsCreator: () => T) {
    let enums = enumsCreator();
    …
}

const FolderVisibility = Enum(()=> 
{
    enum FolderVisibility {
        PUBLIC ='public',
        PRIVATE=  'private'
    }
    return FolderVisibility;
});