Act - Functional Event Sourcing for TypeScript

A c t

TypeScript-first Event Sourcing Framework

Build robust, auditable, and reactive systems with composable state machines, pure functions, and zero runtime bloat.

Install

npm install @rotorsoft/act

Minimal App

import { act, state } from "@rotorsoft/act";
import { z } from "zod";
const Counter = state("Counter", z.object({ count: z.number() }))
  .init(() => ({ count: 0 }))
  .emits({ Incremented: z.object({ amount: z.number() }) })
  .patch({ Incremented: (event, state) => ({ count: state.count + event.data.amount }) })
  .on("increment", z.object({ by: z.number() }))
  .emit((action, state) => ["Incremented", { amount: action.by }])
  .build();
const app = act().with(Counter).build();
await app.do("increment", { stream: "counter1", actor: { id: "1", name: "User" } }, { by: 1 });
console.log(await app.load(Counter, "counter1"));

Run & Explore

Run your app and see the output in your terminal or browser console.

Get Started

Try it in your browser

Open in StackBlitz Source on GitHub

Functional Event Sourcing

Every state change is a pure function of previous state and events. Immutability and replayability by design.

Composable State Machines

Model your domain as composable, strongly-typed state machines. No classes, just functions and data.

TypeScript Native

Type safety and inference everywhere. Catch errors at compile time, not at runtime.

Reactive by Default

Reactions let you build event-driven flows and side effects with ease.

Postgres Adapter Included

Production-ready Postgres adapter for scalable, persistent event storage. Switch between in-memory and Postgres with a single line of code.

Minimal Footprint

Minimal and dependency-light. No codegen, no runtime bloat, and a tiny bundle size.