When building frontends with Javascript, the native localStorage API is super useful for keeping track of state between sessions in the same browser, but it's not as good a solution when your data needs to be shared across multiple devices or browsers.

For instance, let's say you want to show a welcome modal to all new users that sign up for your product. If you use localStorage to track if a user has already seen this modal, your users will end up getting the experience repeatedly every time they switch devices or browsers, or whenever Chrome decides to nuke your data.

I built remoteStorage to help fix that. Using the same API as localStorage, remoteStorage allows you to easily read and write data on the fly while maintaining state across browsers and devices in order to provide a better user experience.

The project is built as a monorepo in Typescript and contains a JS library that works across any Javascript stack (including Node.js and React Native) and is lightweight (~1 kb minified). The server is built with Nest.js with a disk-persisted Redis Database. It can be deployed in a few minutes using Docker.

One of the biggest challenges when building this was coming up with a secure scheme for handling authentication while still keeping the API dead simple for frontend devs to use. While the project is intended to store non-sensitive data like impression events/preferences, I still wanted to make sure data couldn’t easily leak or be tampered with.

One solution has been to generate a unique secret UUID per user on your own backend to identify the user. Alternatively, you could create a simple wrapper/proxy API around remoteStorage that uses your own authentication method to verify the user's identity before allowing them to access the data (this is super simple to build with React Server Components). Then, you could pick a secure and secret Instance ID that is not publicly available to ensure that only your application can access the data.

Has anyone felt the same pain points with localStorage before? Is this solution useful? Let me know what you think or ideas for how I can improve it :)