Use object literal as TypeScript enum values

TypeScript supports numeric or string-based enums only, so you have to emulate object enums with a class (which will allow you to use it as a type in a function declaration):

export class PizzaSize {
  static readonly SMALL  = new PizzaSize('SMALL', 'A small pizza');
  static readonly MEDIUM = new PizzaSize('MEDIUM', 'A medium pizza');
  static readonly LARGE  = new PizzaSize('LARGE', 'A large pizza');

  // private to disallow creating other instances of this type
  private constructor(private readonly key: string, public readonly value: any) {
  }

  toString() {
    return this.key;
  }
}

then you can use the predefined instances to access their value:

const mediumVal = PizzaSize.MEDIUM.value;

or whatever other property/property type you may want to define in a PizzaSize.

and thanks to the toString() overriding, you will also be able to print the enum name/key implicitly from the object:

console.log(PizzaSize.MEDIUM);  // prints 'MEDIUM'