window.IsUSD property not working inside USD

I have used this JavaScript as  it is documented here:

https://msdn.microsoft.com/en-us/library/dn864970.aspx

if ((window.IsUSD != null) && (window.IsUSD == true))
{
   window.open(http://event/?EventName=<EVENT_NAME>&key=value&key=value&…);
}

 However, when I execute the script inside USD, the property window.IsUSD still comes as "undefined"

is anyone having similar problem? Is there another way to identify when client script is running inside USD?