Unions were added in TS 1.4, over a year ago.<p><a href="https:&#x2F;&#x2F;blogs.msdn.microsoft.com&#x2F;typescript&#x2F;2015&#x2F;01&#x2F;16&#x2F;announcing-typescript-1-4&#x2F;" rel="nofollow">https:&#x2F;&#x2F;blogs.msdn.microsoft.com&#x2F;typescript&#x2F;2015&#x2F;01&#x2F;16&#x2F;annou...</a>