You are correct, except this will not work in the significant case where any falsy value is passed ("", 0, null, NaN... I exclude undefined because that is the

You are correct, except this will not work in the significant case where any falsy value is passed ("", 0, null, NaN... I exclude undefined because that is the intended behavior) or with booleans. A slightly more verbose, yet hardy syntax would go like this: function foo(arg1, arg2){ arg1 = arg1 === undefined ? "foo" : arg1; arg2 = arg2 === undefined ? "bar" : arg2; } This would catch the intended behavior, which is to fill a parameter when it is not supplied at all.