What about the ​let​ keyword?

  for (let i = 0; i < 5; i++) {
  setTimeout(function(){
    console.log("i:" + i);
  }, i * 1000);
}

The specs says that ​let​ is bound to each iteration of the ​for​ loop. It's in the spec. 

  for (var i = 0; i < 5; i++) {
  let j = i;
  setTimeout(function(){
    console.log("j:" + j);
  }, i * 1000);
}

Question (from Kyle): is this closure or not?

  var foo = (function(){
  
  var o = { bar : "bar" };
  
  return {obj: o };
  
})();

console.log(foo.obj.bar);   // "bar"

I would say not, because we are not returning a function. Or the the IFEE does not run outside it's original scope.