Install nodenv (rbenv for Node) via homebrew: brew install nodenv. Note the caveats have you add to your .{z,ba}shrc - you’ll need this for it to work.
Node has a pattern of regular major version releases purely based on a calendar schedule, because semantic versioning is for losers apparently.
Even-numbered major versions are the more stable ones which will get long-term support, so in general it’s best to stick to those.
Install Node: nodenv install 14.14.0
Set the Node version for a project in .node-version and nodenv will use it automatically when you’re in that directory or a sub-directory (like rbenv).
npm is the equivalent of bundler.
nodenv will have installed the matching version of npm for you, but if you want to update it, you can always run npm install --global npm@latest to update it.
In a new directory you can then run npm init to create the package.json, which is the equivalent of the Gemfile.
Your default package.json will have a test script defined. You can run this (and any other command you add to scripts) with npm run test (or npm test for short in this case, as one of npm’s built in commands).