9.7 Omitting descriptor properties

All properties of descriptors are optional. What happens when you omit a property depends on the operation.

9.7.1 Omitting descriptor properties when creating properties

When we create a new property via a descriptor, then omitting attributes means that their default values are used:

const car = {};
Object.defineProperty(
  car, 'color', {
    value: 'red',
  });
assert.deepEqual(
  Object.getOwnPropertyDescriptor(car, 'color'),
  {
    value: 'red',
    writable: false,
    enumerable: false,
    configurable: false,
  });

9.7.2 Omitting descriptor properties when changing properties

If instead, we change an existing property, then omitting descriptor properties means that the corresponding attributes are not touched:

const car = {
  color: 'yellow',
};
assert.deepEqual(
  Object.getOwnPropertyDescriptor(car, 'color'),
  {
    value: 'yellow',
    writable: true,
    enumerable: true,
    configurable: true,
  });
Object.defineProperty(
  car, 'color', {
    value: 'pink',
  });
assert.deepEqual(
  Object.getOwnPropertyDescriptor(car, 'color'),
  {
    value: 'pink',
    writable: true,
    enumerable: true,
    configurable: true,
  });