In most modern browsers, you have the option to create a SharedWorker, a type of web worker that, as the name suggests, can be shared across multiple instances of the same page.

For example, imagine you have a Nostr client open in multiple tabs. Instead of each tab acting as a separate client, connecting to relays and listening for events independently, you can use a single shared worker that maintains the connection in the background and updates all tabs as needed.

The problem is that SharedWorker is not supported by every browser.

To work around this issue, I built sharedexecutor-js, a small library that wraps SharedWorker. When SharedWorker isn’t available, it emulates the same behavior by spawning standalone workers connected with a Broadcast Channel, one of the workers is elected as the master while the others proxy their calls through it, effectively acting as a browser-side RPC system (no server needed). If the master dies for any reason, another worker is automatically elected to take its place.

If you want to try it out, i made a small demo that lets you paint a canvas across iframes and tabs: https://rblb.it/sharedexecutor-js/ .