iii-reactive-backend

Original：🇺🇸 English

Translated

Builds reactive real-time backends on the iii engine. Use when building event-driven apps where state changes automatically trigger side effects, clients receive live updates via streams or websockets, or you need a real-time database layer with pub/sub and CRUD endpoints.

3installs

Sourceiii-hq/skills

Added on2026-04-21

NPX Install

npx skill4agent add iii-hq/skills iii-reactive-backend

SKILL.md Content

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Reactive Backend

Comparable to: Convex, Firebase, Supabase, Appwrite

Key Concepts

Use the concepts below when they fit the task. Not every reactive backend needs every trigger or realtime surface shown here.

State is the "database" — CRUD via
```
state::set/get/update/delete/list
```
State triggers fire automatically when any value in a scope changes
Side effects (notifications, metrics, stream pushes) are wired reactively, not imperatively
Streams deliver real-time updates to connected clients

Architecture

text

HTTP CRUD endpoints
  → state::set/update/delete (writes to 'todos' scope)
    ↓ (automatic state triggers)
    → on-change → stream::send (push to clients)
    → update-metrics → state::update (aggregate counters)

HTTP GET /metrics → reads from 'todo-metrics' scope
WebSocket clients ← stream 'todos-live'

iii Primitives Used

Primitive	Purpose
`registerWorker`	Initialize the worker and connect to iii
`registerFunction`	CRUD handlers and reactive side effects
`trigger({ function_id: 'state::...', payload })`	Database layer
`registerTrigger({ type: 'state', config: { scope } })`	React to any change in a scope
`trigger({ ..., action: TriggerAction.Void() })`	Fire-and-forget stream push to clients
`registerTrigger({ type: 'http' })`	REST endpoints

Reference Implementation

See ../references/reactive-backend.js for the full working example — a real-time todo app with CRUD endpoints, automatic change broadcasting via streams, and reactive aggregate metrics.

Common Patterns

Code using this pattern commonly includes, when relevant:

```
registerWorker(url, { workerName })
```
— worker initialization

trigger({ function_id: 'state::set/get', payload: { scope, key, value } })

— CRUD via state module

registerTrigger({ type: 'state', function_id, config: { scope } })

— reactive side effects on state change

Event argument destructuring in reactive handlers:

async (event) => { const { new_value, old_value, key } = event }

trigger({ function_id: 'stream::send', payload, action: TriggerAction.Void() })

— push live updates to clients

```
const logger = new Logger()
```
— structured logging inside handlers

Adapting This Pattern

Use the adaptations below when they apply to the task.

State triggers fire on any change in the scope — use the
```
event
```
argument (
```
new_value
```
,
```
old_value
```
,
```
key
```
) to determine what changed
Multiple functions can react to the same scope independently (on-change and update-metrics both watch
```
todos
```
)

Stream clients connect via

ws://host:port/stream/{stream_name}/{group_id}

Keep reactive functions fast — offload heavy work to queues if needed

Pattern Boundaries

If the request focuses on registering external/legacy HTTP endpoints via
```
registerFunction
```
(especially with endpoint lists like
```
{ path, id }
```
plus iteration), prefer
```
iii-http-invoked-functions
```
.
Stay with
```
iii-reactive-backend
```
when state scopes, state triggers, and live stream updates are the core requirement.

When to Use

Use this skill when the task is primarily about
```
iii-reactive-backend
```
in the iii engine.
Triggers when the request directly asks for this pattern or an equivalent implementation.

Boundaries

Never use this skill as a generic fallback for unrelated tasks.
You must not apply this skill when a more specific iii skill is a better fit.
Always verify environment and safety constraints before applying examples from this skill.