Extending Enum in typescript

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)