I never use null in Javascript, because I don't want attributes of type null, I just want attributes to either be present or not. This usually simplifies all designs and there is no need to think about null separately; it's treated in code an invalid value for an attribute.
The remaining caveat is that when serializing an object, attributes of type undefined need to be skipped, and some libraries get that wrong. So sometimes it is necessary to delete them from objects before serialization.
So in my view, things would be better if null didn't exist at all and if assigning an undefined value to an object attribute would actually delete the attribute from the object. Of course the language can't be changed now, but that is the philosophy I try to use in code design.
I do realize there is the use case of passing an update object e.g. with HTTP PUT/PATCH and wanting to make a distinction between "don't update an attribute" and "remove an attribute". In that case, null kind of makes sense as a designator to remove an attribute.
The remaining caveat is that when serializing an object, attributes of type undefined need to be skipped, and some libraries get that wrong. So sometimes it is necessary to delete them from objects before serialization.
So in my view, things would be better if null didn't exist at all and if assigning an undefined value to an object attribute would actually delete the attribute from the object. Of course the language can't be changed now, but that is the philosophy I try to use in code design.
I do realize there is the use case of passing an update object e.g. with HTTP PUT/PATCH and wanting to make a distinction between "don't update an attribute" and "remove an attribute". In that case, null kind of makes sense as a designator to remove an attribute.