node-steamcommunity is a Node.js module that's designed to interact very simply with the steamcommunity.com website.
SteamID
Many of node-steamcommunity's methods require the SteamID of a thing (user, group, etc.) to act on. When a SteamID is expected, node-steamcommunity requires a SteamID object. The SteamID class is available as a SteamID property of the root node-steamcommunity module.
As an example:
var SteamCommunity = require('steamcommunity');
var SteamID = SteamCommunity.SteamID;
var sid = new SteamID('[U:1:46143802]');
console.log(sid.toString()); // 76561198006409530
This SteamID class is node-steamid. You should use the SteamID available through node-steamcommunity instead of requiring node-steamid yourself since there may be version mismatches.
API Documentation
See the SteamCommunity page to start down the rabbit hole of documentation.