How to Build a Pinterest Notes Extension (Tech Stack + UX Patterns)

For the geeks out there, here is how Notestopin is built.

The Tech Stack

• Vanilla JS: No React, no Vue. Why? Performance. We are injecting into a heavy site; we need to be invisible.
• Shadow DOM: To ensure our styles don't bleed into Pinterest, and theirs don't break ours.
• Chrome Storage API: The local database backend.

The Challenge: Virtualization

Pinterest uses a virtualized masonry grid. DOM elements appear and disappear as you scroll. Attaching buttons to these moving targets was the hardest engineering challenge. We use `MutationObservers` and careful state tracking to ensure the Note button always stays with the right pin.