This repository includes a jarfile. It points to it.

npm install --save-dev selenium-server-standalone-jar

This is up to you. All you get is:

var jar = require('selenium-server-standalone-jar');
console.log(jar.path);    // path to selenium-server-standalone-X.YY.Z.jar
console.log(jar.version); // X.YY.Z

This repository has no advice as to how to run the jar. Other libraries should fill that void; they can depend on this library to keep things simple.