Penpal

A lightweight JavaScript library that streamlines secure, promise-based communication between a parent window and an iframe.

Penpal eliminates the friction of working with the postMessage API by wrapping cross-domain communication in a clean, asynchronous interface. It allows developers to call methods on a child iframe from a parent window (and vice versa) as if they were local functions, handling the serialization and handshake protocols automatically. With over 150,000 weekly downloads on npm, it has become a standard tool for building secure third-party integrations, embedded widgets, and micro-frontend architectures where isolation and security are non-negotiable.

https://github.com/Aaronius/penpal