node-jsdom in buster-backports has unmeetable dependencies

[Nick <debian-backports@njw.name>]

Hi,

I just tried to install node-jsdom from buster-backports, version 
16.4.0+~cs77.17.35-2~bpo10+1, and it fails with this message:

$ apt -s install node-jsdom
NOTE: This is only a simulation!
      apt needs root privileges for real execution.
      Keep also in mind that locking is deactivated,
      so don't depend on the relevance to the real current 
situation!
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 node-jsdom : Depends: node-webidl-conversions but it is not 
installable
E: Unable to correct problems, you have held broken packages.

I have a pretty vanilla and up to date debian buster install in 
general. I presume I'm not doing anything wrong, but I could be 
wrong; please set me straight if this is my fault!

If not, can the node-webidl-conversions package either be added to 
backports or removed from Depends (if safe), so the package can be 
made to work?

Thanks,

Nick