for-of loop compiled with Babel, both with and without "loose" mode

for-of-loose.js

for (var _iterator = foo(), _isArray = Array.isArray(_iterator), _i = 0, _iterator = _isArray ? _iterator : _iterator[Symbol.iterator]();;) {
  var _ref;

  if (_isArray) {
    if (_i >= _iterator.length) break;
    _ref = _iterator[_i++];
  } else {
    _i = _iterator.next();
    if (_i.done) break;
    _ref = _i.value;
  }

  var x = _ref;

  console.log(x);
}

for-of-strict.js

var _temporalUndefined = {};

function _temporalAssertDefined(val, name, undef) { if (val === undef) { throw new ReferenceError(name + " is not defined - temporal dead zone"); } return true; }

for (var _iterator = foo(), _isArray = Array.isArray(_iterator), _i = 0, _iterator = _isArray ? _iterator : _iterator[Symbol.iterator]();;) {
  var x = _temporalUndefined;

  var _ref;

  if (_isArray) {
    if (_i >= _iterator.length) break;
    _ref = _iterator[_i++];
  } else {
    _i = _iterator.next();
    if (_i.done) break;
    _ref = _i.value;
  }

  x = _ref;

  console.log(_temporalAssertDefined(x, "x", _temporalUndefined) && x);
}