[ben_alman]

And this behavior is totally obvious (not)

  var id = 123;
  function updateOptionalProperty(obj) {
    with (obj) {
      id = 456;
    }
  }

  updateOptionalProperty({id: 0});
  id // 123

  updateOptionalProperty({});
  id // 456

[bmuon]

I actually ran into code once that had a variable named "position" (totally common name) and then used "with" on a node's style property to set another style based on the value of this "position" variable. Instant bug. It took me a while to figure out what was going on.