var f0 = function (a, b = a, c = b) {
  return [a, b, c];
};

expect(f0(1)).toEqual([1, 1, 1]);

var f1 = function ({a}, b = a, c = b) {
  return [a, b, c];
};

expect(f1({a: 1})).toEqual([1, 1, 1]);

var f2 = function ({a}, b = a, c = a) {
  return [a, b, c];
};

expect(f2({a: 1})).toEqual([1, 1, 1]);