nominalTyping.ts

namespace Literal {
  /** Generic Id type */
  type Id<T extends string> = {
    type: T,
    value: string,
  }

  /** Specific Id types */
  type FooId = Id<'foo'>;
  type BarId = Id<'bar'>;

  /** Optional: contructors functions */
  const createFoo = (value: string): FooId => ({ type: 'foo', value });
  const createBar = (value: string): BarId => ({ type: 'bar', value });

  let foo = createFoo('sample')
  let bar = createBar('sample');

  foo = bar; // Error
  foo = foo; // Okay
}

namespace EnumDriven {
  // FOO
  enum FooIdBrand { }
  type FooId = FooIdBrand & string;

  // BAR
  enum BarIdBrand { }
  type BarId = BarIdBrand & string;

  /**
   * Usage Demo
   */
  var fooId: FooId;
  var barId: BarId;

  // Safety!
  fooId = barId; // error
  barId = fooId; // error

  // Newing up
  fooId = 'foo' as FooId;
  barId = 'bar' as BarId;

  // Both types are compatible with the base
  var str: string;
  str = fooId;
  str = barId;
}

namespace Interface {

  // FOO
  interface FooId extends String {
    _fooIdBrand: string; // To prevent type errors
  }

  // BAR
  interface BarId extends String {
    _barIdBrand: string; // To prevent type errors
  }

  /**
   * Usage Demo
   */
  var fooId: FooId;
  var barId: BarId;

  // Safety!
  fooId = barId; // error
  barId = fooId; // error
  fooId = <FooId>barId; // error
  barId = <BarId>fooId; // error

  // Newing up
  fooId = 'foo' as any;
  barId = 'bar' as any;

  // If you need the base string
  var str: string;
  str = fooId as any;
  str = barId as any;
}