Array of enums from enum value strings

Question

I'm trying to convert enum value strings to actual enums. I know you can just compare a string and be done with it (e.g. MyEnum.FirstEnum === 'My_First_Enum' would return true), but it would be nice if I can return enums instead of strings.

export enum MyEnum {
  FirstEnum = 'My_First_Enum',
  SecondEnum = 'My_Second_Enum',
  ThirdEnum = 'My_Third_Enum'
}

getMyEnums(): MyEnum[] {
  // These would be an input argument, but for the sake of this example, I thought this was easier to understand
  const stringEnumValues = ['My_Second_Enum', 'My_Third_Enum'];

  // Convert to enums (result is [undefined, undefined])
  return stringEnumValues.map(e => MyEnum[e]);
}

Answer 1

Try to use Object.entries method, then filter by your desired values stringEnumValues and then just map filtered values:

const stringEnumValues = ['My_Second_Enum', 'My_Third_Enum'];  
let result = Object.entries(MyEnum)
                      .filter(([k,v])=> stringEnumValues.includes(v))
                      .map(([ke, vl]) => MyEnum[ke]);

A work example at stackblitz can be seen here.

Answer 2

You need to cast your string as a key of the enum type, here is how to do it both with an array of strings that represent the enum keys and with an array of strings that represent the values:

Get by keys:

getMyEnums(): MyEnum[] {

  const stringEnumValues = ['SecondEnum', 'ThirdEnum'];  
  return stringEnumValues.map( (e : keyof typeof MyEnum) => MyEnum[e])

}

Get by values:

getMyEnums2(): MyEnum[] {

  const stringEnumValues = ['My_First_Enum', 'My_Second_Enum'];  
  return stringEnumValues.map( (e : MyEnum) => e)

}

Example: https://stackblitz.com/edit/angular-yd6yhe?file=src/app/app.component.ts

Source: https://blog.mikeski.net/development/javascript/typescript-enums-to-from-string/

Answer 3

Why not try a freezed JSON hash for this purpose?

export const MyEnum = Object.freeze({
  'FirstEnum': 'My_First_Enum',
  'SeconfEnum': 'My_Second_Enum',
  'ThirdEnum': 'My_Third_Enum',
  'My_First_Enum': 'FirstEnum',
  'My_Second_Enum': 'SeconfEnum',
  'My_Third_Enum': 'ThirdEnum'
});