I'm afraid that this post, while well intentioned, is actually clouding the issue it's attempting to clarify.

It demonstrates that CoffeeScript's `do` feature provides a convenient way to create a new scope for particular variables (a thing only possible in JavaScript via an immediately-invoked-function, at least, until `let` arrives) ... which is true, but is also an orthogonal concern to whether or not CoffeeScript's normal mode of variable scoping is lexical.

In many of the examples in this post:

    do (foo = 'outer') ->
      do (foo = 'inner') ->

... all of the variables are local to their function, making it a moot question whether the language is dynamic or lexical. Just as in JavaScript:

    function() { 
      var foo = "outer";
      function() {
        var foo = "inner";
      }
    }

... it would make no difference if the language had lexical or dynamic scope, because there are no variables present here that would need to reach outside of their enclosing function in order to perform variable lookup.

Lexical vs. dynamic scoping only comes into play when you refer to an external variable. Whether or not that variable is or can be shadowed is beside the point. Putting parameters aside ... In JavaScript, the variable's identity is the closest "var"-declaration of that variable. In CoffeeScript, the variable's identity is simply the name of that variable, wherever it might occur in the current lexical scope. Both ways are lexical, not dynamic.