No, unfortunately. If a reference isn't found in your context object, it falls through to the ambient namespace. So say you run ... context = { foo: 1, b

No, unfortunately. If a reference isn't found in your context object, it falls through to the ambient namespace. So say you run ... context = { foo: 1, bar: 2 }; with (context) { foo = 2; bar = 3; } That will probably do what you expect. But now say you run it where context is just ... context = { foo: 1 }; with (context) { foo = 2; bar = 3; } ... you might think this would add a 'bar' property to your context object, but in fact it creates a global variable bar. Whoops! In short, 'with' is pointy on both ends.