Once you've created an account, the Napkin editor allows you to install any NPM module or package.
Currently, all installed NPM modules are shared across a user's functions. Just install a module once and it will be there ready to use in any of your other functions. Currently, combined module storage space is limited to 250MB.
Napkin supports both CommonJS and ES6 module syntax, so both of the following work:
import _ from "lodash"; // or const _ = require("lodash");