Object.hasOwn(): existing field with undefined

Useful to know

Object.hasOwn(obj, key) checks whether the property belongs to the object itself. For {price: undefined}, check for "price" returns true, despite value undefined. Inherited properties do not pass . [1]

This is useful in a partial update, when a missing field means "do not change", and a filed field has a separate meaning. After the availability check, validate the value as well. Do not use obj.price's truthfulness for the same task: zero, empty string, and false can be consciously submitted eligible data.