Yes but... I don't envy those who would have to maintain and publish several subsets of the Javascript language. And you would almost certainly have to specify

Yes but... I don't envy those who would have to maintain and publish several subsets of the Javascript language. And you would almost certainly have to specify in the source code which version of the language you wanted to adhere too. You couldn't assume it would be the latest, because that would break your code in the future, when the latest version has deprecated whatever feature you relied upon way back. Ugly no matter how you look at it.