TypeScript enums at the type and value level

foo.ts

{
  // Enums represent types and values
  // At the type level, this is a union of all enum members
  // At the value level, this is an object containing enum members
  enum TypeEnum {
    foo,
    bar,
    baz,
  }

  // To access the object type of an enum, we use `typeof <value>`, where `<value>` is the enum
  // object value.
  type TypeObject = typeof TypeEnum;

  // Type level
  type MyObject = {
    // Union of all enum members
    type: TypeEnum;
    // Object containing enum members
    types: TypeObject;
  };

  // Value level
  const myObject: MyObject = {
    // Single enum member
    type: TypeEnum.bar,
    // Object containing enum members
    types: TypeEnum,
  };

  
  // As well as being able to express the type of the enum object from the enum, we can also go the
  // other way: express the type of the enum union from the enum object. Example:
  type ObjectKeys<Object> = Object[keyof Object];
  type TypeEnumFromObject = ObjectKeys<TypeObject>;
  const myType: TypeEnumFromObject = TypeEnum.bar;
}