Block scoping of 'let' in for loop

javascript

"use strict";
var stack = [];

for (let i = 0; i < 10; i++) {
    console.log("inner: " + i);
    i += 4;
    stack.push(() => console.log("outer: " + i));
}

stack.forEach(f => f());

output - Babel

inner: 0
inner: 1
inner: 2
inner: 3
inner: 4
inner: 5
inner: 6
inner: 7
inner: 8
inner: 9
outer: 4
outer: 5
outer: 6
outer: 7
outer: 8
outer: 9
outer: 10
outer: 11
outer: 12
outer: 13

output - Babel without outer

"use strict";
var stack = [];

for (let i = 0; i < 10; i++) {
    console.log("inner: " + i);
    i += 4;
    // stack.push(() => console.log("outer: " + i));
}

stack.forEach(f => f()); 

// Output:
// inner: 0
// inner: 5

output - Firefox 36.0.4

"inner: 0"
"inner: 5"
"outer: 10"
"outer: 10"

output - Node.js

node --version
v0.12.0
node --harmony for-let.js
inner: 0
inner: 5
outer: 4
outer: 9