Engineering glossary

The small, ephemeral channel that broadcasts presence information — cursor positions, user names, colour assignments — alongside the durable document edits in a CRDT-backed editor.

A family of data structures that let multiple users edit the same document offline and still merge into a consistent state when they reconnect.

The two roles in a classic pair-programming session — one types, the other thinks ahead — and the small protocol that keeps them from stepping on each other.

A small declarative language that runs on Google's servers to decide whether each Firestore read or write is allowed — the layer that turns Firebase from a public database into a multi-tenant one.

The process where a server-rendered HTML page becomes interactive in the browser — React attaches event listeners, restores state, and takes over the DOM the server produced.

The protocol WebRTC uses to discover the best network path between two peers, given that one or both of them are likely behind a NAT or firewall.

A compact, signed token format used to carry identity and claims between a client and an API — the format Firebase Authentication issues to every signed-in user.

A fixed-size cache that evicts whichever entry was accessed longest ago — the canonical data-structure interview question and a genuinely useful production primitive.

The middleware on a home or office router that maps many private IP addresses to one public address — and the reason peer-to-peer connections need ICE, STUN, and TURN to find each other.

An older approach to real-time collaborative editing that resolves conflicts by transforming operations relative to each other through a central server — historically powered Google Docs.

A long-lived credential a client exchanges for a fresh short-lived access token (a JWT, in Firebase's case) — the mechanism that keeps users logged in across sessions.

A plain-text format that describes what a media session looks like — codecs, encryption parameters, network addresses — so two WebRTC peers can agree on how to talk to each other.

A compact summary of what a CRDT replica has seen — used to figure out exactly which updates a peer is missing without re-sending the entire document.

A lightweight protocol that lets a peer behind a NAT discover its own public IP address, so it can advertise that address to the other side of a WebRTC call.

In a CRDT, a marker left behind when a character is deleted — kept around so concurrent edits referencing the deleted character can still be ordered correctly.

A relay server that carries WebRTC media on behalf of two peers when they can't reach each other directly — the last resort when STUN fails.

A browser API and protocol stack that lets two browsers exchange audio, video, and arbitrary data peer-to-peer without a media server in the middle.

A long-lived, bidirectional connection between a browser and a server — the transport that makes server-pushed updates feel real-time without polling.

An operation-based CRDT library for JavaScript that powers most of the production-grade collaborative editors built in the browser today, including ShareCode's editor.