An even better question is why not get rid of var and make every variable local to its parent function? To alter globals, use the window object explicitly.
I agree, but I think the solution is to stop using `var`, the question is how useful `var` really is. `let`'s scoping is what it appears to be, `var`'s is not. So `let` is the better choice.
But in practice, there are many cases when I have to create multiple callbacks in a loop; half the time I forget that, in Javascript, declaring a variable inside a loop does not actually create a variable local to the loop, and so have to keep debugging why all my callbacks are behaving exactly the same.
The let statement appears to adopt Lua-style lexical scoping, which will be a breath of fresh air once I can rely on browser support.
const is a different case, but IMO there's no need to use var when let exists.
JS is used in non-DOM contexts as well. Though, of course, if that big a change is being made, a generic substitute for `window` could also be specified.
Isn't that just |this| at the top level?
In node, there is a name for the default global: "global", which is also the default context. So node gives it a "generic substitute" as the OP suggested. Most people use "this" to make assignments to it, rather than the "global" name, since it is usually accessed from the default context.