in memory localStorage polyfill for node.js utilizing ES6 proxies(requires node.js 6 at least)
npm i localstorage-polyfill -D
Saving for development, because primarily this package is meant for unit testing browser in node.js.
require('localstorage-polyfill') // or import 'localstorage-polyfill' global.localStorage // now has your in memory localStorage
For API doc, refer to MDN.
There are other packages like node-localStorage, but none of them work properly when you do
localStorage.c = 1
They only shim the methods of localStorage object, they don't imitate it's behaviour fully.