gistfile1.js

function baseline() {
  var j = 0;
  for (var i = 0; i < 1e7; i++) j = i;
  for (var i = 0; i < 1e7; i++) j = i;
  for (var i = 0; i < 1e7; i++) j = i;
  for (var i = 0; i < 1e7; i++) j = i;
}

function with_with() {
  with ({}) { }

  var j = 0;
  for (var i = 0; i < 1e7; i++) j = i;
  for (var i = 0; i < 1e7; i++) j = i;
  for (var i = 0; i < 1e7; i++) j = i;
  for (var i = 0; i < 1e7; i++) j = i;

}

function m(f) {
  var start = Date.now();
  f();
  var end = Date.now();
  print(f.name + " " + (end - start));
}

m(baseline);
m(with_with);