[ajanuary]

They are in the same lexical scope.

Inside a lexical scope, all matching variable names refer to the same variable. Because they are in the same lexical scope, all instances of the variable name "x" refer to the same variable.

Separate (but related) to this is the concept of where it is valid to dereference variables (this is where my knowledge breaks down - is there an accepted term for this?). Javascript says that for variables declared with "var", it is always valid to dereference them, but it might dereference to "undefined". For variables declared with "let", it is only valid to dereference variables in the lexical scope. In addition to this, it defines a "temporal dead zone", which covers the span between the start of the lexical scope and the "let" declaration. This isn't a novel thing - other languages do it, though they may use different terminology.

It's this "temporal dead zone" that you seem to be referring to when you say it's creating a new implicit scope.

It's still impossible for a let declaration to affect anything outside of its lexical scope. If it's shadowing a variable name in a parent scope, what it can do is stop variable names earlier in the scope from referring to the parent scope and make it refer to the variable in inner scope. This may seem like a problem, but most other languages will do the same thing (C++, Java, C#, Python, Ruby etc.) and I've never seen it be much of an issue.