LwwRegister

Last-Write-Wins Register. Holds a single value; concurrent writes resolve by HLC timestamp.

A LwwRegister (Last-Write-Wins Register) holds a single value. When two clients write concurrently, the write with the higher HLC (Hybrid Logical Clock) timestamp wins. Ties are broken by client ID.

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Usage without schema

const title = client.lwwregister("lw:doc-title");

title.set("My document");

console.log(title.value()); // "My document" | null

title.onChange(v => console.log("title:", v));

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Usage with schema

import { Schema } from "effect";

const Profile = Schema.Struct({
  name: Schema.String,
  avatar: Schema.String,
});

const profile = client.lwwregister("lw:user-42-profile", Profile);

profile.set({ name: "Chahine", avatar: "https://..." });

profile.onChange(v => {
  // v: { name: string; avatar: string } | null
  if (v) console.log("name:", v.name);
});

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API

Method	Description
set(value: T)	Write a new value
value()	Returns current value or null if not set
meta()	Returns { updatedAtMs: number; author: number } | null — timestamp and author of the winning write
onChange(fn)	Subscribe — returns unsubscribe function
stream()	Returns an Effect Stream<T | null> that emits on every change

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Conflict resolution

Conflicts are resolved by HLC timestamp (wall clock + logical counter). The write with the highest timestamp wins. If timestamps are equal, the write from the highest client_id wins. This is deterministic and consistent across all replicas.