Extending Enum in typescript

Question

I was hoping to reuse certain values in enum. Any suggestions of how to achieve such functionality.

enum someEnum {
    a = 'Some String',
    b = 2,
};

enum extendedEnum {
    c = 'string',
    b = someEnum.b
}

type someEnumType<T extends someEnum> = T extends someEnum.a ? string :
    T extends someEnum.b ? number : never;

type extendedEnumType<T extends extendedEnum> =
    T extends extendedEnum.c ? string:          // Gives Error
    T extends extendedEnum.b ? number : never;  // Gives Error

Answer 1

Currently, You can't extend enum in TypeScript

Another option is to use type:

enum Color1 {
    Red = "Red",
    Green = "Green"
}

enum Color2 {
    Yellow = "Yellow",
    Blue = "Blue"
}

define a new type named Colors :

type Colors = Color1 | Color2;

Then you can use it as below :

class AppComponent {
    public color: Colors;
    
    ngOnInit(): void {
      const Colors = { ...Color2, ...Color1 };
      this.color = Colors.Red; // Colors.Green or Colors.Yellow or Colors.Blue
    }
}

Stackblitz Here (Angular)

Stackblitz Here (Typescript)