The apt-get version of node is incredibly old, and installing a new copy is a bit of a runaround.
So here's how you can use NVM to quickly get a fresh copy of Node on your new Bash on Windows install
$ touch ~/.bashrc
$ curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.35.3/install.sh | bash
// restart bash
$ nvm install --lts
Once you've done that you'll get a nice:
$ node --version
$ v12.18.3
I had some trouble on a fresh install of Windows 10 Pro using this script, but found this instruction by NodeSource to be working well, installing the latest nodejs (v10 currently). It's also just two commands:
https://github.com/nodesource/distributions#debinstall