The best nominal typing solution as of TS 3.9.x

1-nominal-types.ts

export declare const nominalTag: unique symbol

type UniqueTypes = string | number | symbol | boolean

/**
 * Needs no validation nominal types
 * (allows the base type T to be uplifted without a cast)
*/
export type Unique<T, M extends UniqueTypes> = T & { [nominalTag]?: M }

/**
 * Validated nominal type
 * (requires the base type T to be uplifted with a cast, ideally after validation)
*/
export type Validated<T, M extends UniqueTypes> = T & { [nominalTag]: M }

2-example-usage.ts

// Usage

// Declared enums used here, but any literal type would work (strings, numbers, unique symbols)
declare enum IdType { }
declare enum AccountBalanceType { }

type Id = Unique<number, IdType>
type AccountBalance = Unique<number, AccountBalanceType>

let id: Id = 123456789; // Raw values of type T are assignable to the Unique subtype
let balance: AccountBalance = 789;

id = balance; // Different types are not equivalent
// ERROR: Type 'Unique<number, AccountBalanceType>' is not assignable to type 'Unique<number, IdType>'

// Translations between Unique and Validated
type ValidatedId = Validated<number, IdType>
let validId: ValidatedId = 123 // Raw values of type T not assignable to validated
// ERROR: Type '123' is not assignable to type 'Validated<number, IdType>'.
validId = id; // Unique not assignable to Validated
// ERROR: Type 'Unique<number, IdType>' is not assignable to type 'Validated<number, IdType>'
validId = 12345 as ValidatedId // Casts "validate" as expected
id = validId // And validated types are exchangable with their "unique" subtypes as expected

// validId. // Nominal tag does not show up in the dotted auto-complete

// Use private fields for class nominality instead of Unique (doesn't work at all)
// or Validated(works but requires boilerplate)
class Point {
    private [nominalTag]: never;
    constructor(public x: number, public y: number){}
}

class Foo {
    private [nominalTag]: never;
    constructor(public x: number, public y: number){}
}

var x: Point = new Point(1, 2);
var y: Foo = new Foo(1, 2);

x = y;
// ERROR: Types have separate declarations of a private property '[nominalTag]'