[z3t4]

I find hoisting a convenient feature as I can declare the variable in context to where it's used. It means I do not have to break the flow of how the code reads, making the code easier to understand and less bug prone. Example:

    if(something) var foo = 1;

[heavenlyblue]

So how do you maintain the invariant that this variable is used only if <something> is true _down the line_?

[z3t4]

It's only logical that it will be undefined if it's never assigned. With var you can just declare anywhere. While with let it feels like a chore when you have to declare in a parent block, eg. outside the if-block for it to be accessible within another if-block. Lexical function scope works very well in an async language with first class functions, as you deal mostly with functions, which can access it's closures at any time, etc. makes it logical that the function should define the scope, not if-statement or for-loops.