I agree with this wholeheartedly--Scheme use an extremely simple scoping model that is nonetheless more expressive than Python (before 3, I guess) and CoffeeScript's. In fact, I only really completely understood JavaScript's model--and realized that, even if a little awkward, it was fundamentally elegant--after writing a Scheme interpreter.
I think Python's is deliberately unexpressive, forcing you to use local variables pretty much everywhere. This tends to decouple stuff, which is usually good. The model is "everything you do is local, unless you know better, and want to jump through a lot of hoops". Coffeescript works a similar way.
Javascript seems to have the model "everything you do is global, unless you know better".
I'm not a big Javascript hater, but this is one very sore point.
He is talking about if you don't do anything extra (in this case, use the var keyword). Much like the nonlocal keyword in Python requires knowing about it and wanting to use it in order to actually use it and get the non-default behavior.
'let' is a way to make things more local! When I say: let x = 0, I'm saying "hey, I don't care what 'x' is in other scopes, in this local scope it's 10, dammit!"
No, the Javascript model is "you name things with `var`, you mutate things with `=`".
Python went for a more complicated scheme of having every variable in a function be a new binding when first assigned, and then it's just mutation (i.e. 'local'), unless explicitly declared to be nonlocal, but it still makes sense with their... penchant for mutable state.
And Coffescript instead went over to PHP to have some of the glue it was eating.
Scheme dates to about 1975. But there were older languages with this kind of scoping, like John Reynolds' Gedanken and Landin's ISWIM. (I guess I wouldn't count Algol-60 since it was call-by-name.)
