# @moq/json [](https://www.npmjs.com/package/@moq/json) [](https://www.typescriptlang.org/) JSON publishing over [Media over QUIC](https://moq.dev/) tracks, in two modes: - **`Snapshot`**: lossy. One JSON value updated over time; a consumer only gets the most recent value. Intermediate updates are collapsed and older groups are dropped. - **`Stream`**: lossless. An ordered append-log of self-contained records; every record is preserved and delivered in order, nothing is ever superseded. Pick `Snapshot` when consumers care about "what is the value now" (a catalog, a status document) and `Stream` when they care about every record (an event log, a media timeline). ## Quick Start ```bash bun add @moq/json ``` ### Snapshot: the latest value A JSON value is published over a [`@moq/net`](../net) track as a series of groups. Each group is self-contained: its first frame is a full snapshot and any following frames are [RFC 7396 JSON Merge Patch](https://www.rfc-editor.org/rfc/rfc7396.html) deltas applied in order. A consumer jumps to the newest group, reads the snapshot, and applies the deltas, so a late joiner never needs older groups. This is lossy by design: only the most recent value is delivered. ```ts import { Snapshot } from "@moq/json"; // Publish: each update supersedes the last. const producer = new Snapshot.Producer(track); producer.update({ hello: "world" }); // Consume: yields the latest reconstructed value, collapsing any backlog. const consumer = new Snapshot.Consumer(track); for await (const value of consumer) { console.log(value); } ``` Pass `{ deltaRatio: x }` with a positive `x` to `Snapshot.Producer` to emit merge-patch deltas. A new snapshot group rolls once the deltas *already written* to the group exceed `x` times the fresh snapshot size; the delta that crosses the budget still lands first, so a group overshoots by at most one delta. `deltaRatio` defaults to `8` when unset. Set it to `0` to disable deltas: every change becomes a fresh single-frame snapshot group. Arrays are replaced wholesale within a delta; a value set to `null` falls back to a snapshot, since merge patch reads `null` as a key deletion. ### Stream: every record An ordered log of self-contained records, one JSON value per frame, all riding a single group. Nothing is superseded: a consumer yields every record in order. ```ts import { Stream } from "@moq/json"; const producer = new Stream.Producer(track); producer.append({ event: "started" }); producer.append({ event: "stopped" }); const consumer = new Stream.Consumer(track); for await (const record of consumer) { console.log(record); } ``` Both modes support optional group-scoped DEFLATE compression (`{ compression: true }` on both sides), interoperable with the Rust `moq-json` crate.