Typescript - Exclude enum values with function

Question

I'm trying to filter out enum values and I have some issues with typings/filtering these entries. I cannot type my filter function correctly. I spent some hours and I have no idea how to do it.

What I want to achieve:

I have enum like:

enum AllEntries {
    A = 'a',
    B = 'b',
    C = 'c',
    D = 'd'
}

And I want to have this enum to have some entries filtered out for some keys in array:

const testObject = {
    // this one should have possibility to access all enum keys except A
    withoutA: filterEnum(AllEntries, [AllEntries.A]),

    // this one should have possibility to access all enum keys except A
    all: AllEntries,

    // this one should have possibility to access only D entry
    onlyD: filterEnum(AllEntries, [AllEntries.A, AllEntries.B, AllEntries.D])
}

I want function filterEnum to return "clone" of AllEntries without values given in second parameter, also it shouldn't allow me to access eg. A key in testObject.withoutA

I'm trying to use Exclude utility type etc, but with no results. Do you have any ideas?

Example code that shows what I want to achieve (with nasty any):

here

captain-yossarian from Ukraine · Accepted Answer · 2021-05-04 09:12:53Z

1

First of all, there is no dynamic Enums.

It is better to use immutable objects instead of enums, because have issues with number values.

const All = {
  A: 'a',
  B: 'b',
  C: 'c'
} as const;

type All = typeof All;

const remove = <T, P extends keyof T>(obj: T, prop: P) => {
  const { [prop]: _, ...rest } = obj;
  return rest
}

const filterOut = <T extends keyof All>(obj: All, exclude: T[]): Omit<All, T> =>
  exclude.reduce(remove, obj as any)


const withoutA = filterOut(All, ['A']); // ok
const onlyC = filterOut(All, ['A', 'B']) // ok

It is hard to make reduce in TS without type casting (as operator)

Playground

edited May 4, 2021 at 9:12

answered Apr 21, 2021 at 18:54

captain-yossarian from Ukraine

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1 Comment

Organic Over a year ago

It's insanity that there isn't an easier way to manipulate enums!

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