(function(x, f = () => x) {
  var x;
  var y = x;
  x = 2;
  return [x, y, f()];
})(1)

(function() {
  return [
    (() => this.x).bind({ x: 'inner' })(),
    (() => this.x)()
  ]
}).call({ x: 'outer' });

typeof (function* f() { yield f })().next().next()