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@moeru/eventa

Transport-aware events powering ergonomic RPC and streaming flows.

Core Concepts

Eventa is built around three ideas:

1. Events are first-class — define typed events once, use them everywhere
2. Transports are swappable — the same event definitions work across Electron IPC, WebSocket, Web Workers, BroadcastChannel, EventEmitter, EventTarget, and Worker Threads
3. RPC is just events — invoke/stream patterns are composed from the same event primitives

API Quick Reference

Event Definition & Context

import { createContext, defineEventa } from '@moeru/eventa'

// Define a typed event (the generic is the payload type)
const move = defineEventa<{ x: number, y: number }>()

// Create a base context (in-memory, useful for same-process communication)
const ctx = createContext()

// Emit and listen
ctx.emit(move, { x: 100, y: 200 })
ctx.on(move, ({ body }) => console.log(body.x, body.y))

Unary RPC (Invoke)

import { createContext, defineInvoke, defineInvokeEventa, defineInvokeHandler } from '@moeru/eventa'

const ctx = createContext()

// defineInvokeEventa<ResponseType, RequestType>(optionalName)
const echo = defineInvokeEventa<{ output: string }, { input: string }>('rpc:echo')

// Register handler (server side)
defineInvokeHandler(ctx, echo, ({ input }) => ({ output: input.toUpperCase() }))

// Create invoke function (client side)
const invokeEcho = defineInvoke(ctx, echo)
const result = await invokeEcho({ input: 'hello' }) // { output: 'HELLO' }

Streaming RPC (Server-Streaming)

import { createContext, defineInvokeEventa, defineStreamInvoke, defineStreamInvokeHandler, toStreamHandler } from '@moeru/eventa'

const ctx = createContext()
const sync = defineInvokeEventa<
  { type: 'progress' | 'result', value: number },
  { jobId: string }
>('rpc:sync')

// Generator-style handler
defineStreamInvokeHandler(ctx, sync, async function* ({ jobId }) {
  for (let i = 1; i <= 5; i++) {
    yield { type: 'progress' as const, value: i * 20 }
  }
  yield { type: 'result' as const, value: 100 }
})

// Or imperative style with toStreamHandler
defineStreamInvokeHandler(ctx, sync, toStreamHandler(async ({ payload, emit }) => {
  emit({ type: 'progress', value: 0 })
  emit({ type: 'result', value: 100 })
}))

// Consume as async iterator
const stream = defineStreamInvoke(ctx, sync)
for await (const update of stream({ jobId: 'import' })) {
  console.log(update.type, update.value)
}