The argument for not introducing a 'var' keyword equivalent seems to be "Javascript's implementation sucks", completely glossing over the fact that really it's

The argument for not introducing a 'var' keyword equivalent seems to be "Javascript's implementation sucks", completely glossing over the fact that really it's the lack of block scoping and the presence of undefined that leads to variable 'hoisting' and related issues. CoffeeScript removes the latter, and the former is a lot easier to introduce once you have explicit variable declaration. Seems kinda a circular argument to me.