gistfile1.txt

function bad (foo) {
  if ( ! (foo instanceof Bar) ) {
    throw new TypeError("This is an annoying restriction!");
  }
  return foo.baz(foo.quux(10));
}

function good (foo) {
  if ( !foo.baz || !foo.quux ) {
    throw new TypeError("We need foo to have baz and quux methods.");
  }
  return foo.baz(foo.quux(10));
}