@llui/effects

Effect builders for LLui. Effects are data -- update() returns them, the runtime dispatches.

pnpm add @llui/effects

Usage

import { http, cancel, debounce, handleEffects } from '@llui/effects'

// Debounced search with cancel
function update(state: State, msg: Msg): [State, Effect[]] {
  switch (msg.type) {
    case 'search':
      return [
        { ...state, query: msg.value },
        [
          cancel('search'),
          debounce(
            'search',
            300,
            http({
              url: `/api/search?q=${msg.value}`,
              onSuccess: (data) => ({ type: 'results', data }),
              onError: (err) => ({ type: 'searchError', err }),
            }),
          ),
        ],
      ]
  }
}

// Wire up in component
const handler = handleEffects<Effect, Msg>()
  .use(httpPlugin)
  .else((effect, send) => {
    /* custom effects */
  })

API

Effect Builders

Function	Description
`http({ url, onSuccess, onError })`	HTTP request effect
`cancel(token, inner?)`	Cancel by token, optionally replace with inner
`debounce(key, ms, inner)`	Debounce inner effect by key
`timeout(ms, msg)`	Fire msg after delay
`interval(ms, msg)`	Fire msg on interval
`storageSet(key, value, storage?)`	Write to localStorage/sessionStorage
`storageGet(key, onResult, storage?)`	Read from storage
`storageRemove(key, storage?)`	Remove from storage
`storageWatch(key, onChange)`	Watch storage for changes
`broadcast(channel, data)`	Send on BroadcastChannel
`broadcastListen(channel, onMsg)`	Listen on BroadcastChannel
`sequence([...effects])`	Run effects in order
`race([...effects])`	Run effects concurrently, first wins
`upload({ url, body, onProgress, onSuccess, onError })`	File upload with progress via XHR
`clipboardRead({ onSuccess, onError })`	Read text from clipboard
`clipboardWrite(text)`	Write text to clipboard (fire-and-forget)
`notification(title, opts?)`	Show browser notification (requests permission)
`geolocation({ onSuccess, onError, enableHighAccuracy? })`	One-shot geolocation position

Upload

Upload files with progress tracking via XMLHttpRequest:

import { upload } from '@llui/effects'

const effect = upload({
  url: '/api/upload',
  body: formData,
  headers: { Authorization: `Bearer ${token}` },
  onProgress: (loaded, total) => ({
    type: 'uploadProgress',
    pct: Math.round((loaded / total) * 100),
  }),
  onSuccess: (data, status) => ({ type: 'uploadDone', data, status }),
  onError: (error) => ({ type: 'uploadFailed', error }),
})

Clipboard

Read and write text via the Clipboard API:

import { clipboardRead, clipboardWrite } from '@llui/effects'

// Copy text to clipboard (fire-and-forget)
clipboardWrite('Hello, world!')

// Read text from clipboard
clipboardRead({
  onSuccess: (text) => ({ type: 'pasted', text }),
  onError: (error) => ({ type: 'clipError', error }),
})

Notification

Show browser notifications (requests permission automatically):

import { notification } from '@llui/effects'

notification('New message', {
  body: 'You have a new message from Alice',
  icon: '/avatar.png',
  onClick: () => ({ type: 'openChat' }),
  onError: () => ({ type: 'notifBlocked' }),
})

Geolocation

One-shot position request:

import { geolocation } from '@llui/effects'

geolocation({
  enableHighAccuracy: true,
  onSuccess: (pos) => ({
    type: 'located',
    lat: pos.latitude,
    lng: pos.longitude,
  }),
  onError: (error) => ({ type: 'geoError', error }),
})

Effect Handling

Function	Description
`handleEffects<E, M>()`	Chainable effect handler builder
`.use(plugin)`	Add an effect handler plugin
`.else(handler)`	Fallback for unhandled effects
`resolveEffects(def)`	SSR data loading -- resolves effects server-side

Types

Type	Description
`Async<T, E>`	`idle \| loading \| success \| failure` -- async data state
`ApiError`	`network \| timeout \| notfound \| unauthorized \| forbidden \| ratelimit \| validation \| server`

Functions

`_getEffectInterceptor()`

@internal consumed by @llui/dom's effect-dispatch wrapper.

function _getEffectInterceptor(): EffectInterceptor

Dev-only hook reserved for Phase 2 use. No-op in production — setting this is a developer opt-in. When null, callers skip the check entirely so there is zero allocation on the hot path. Phase 1 reality: @llui/dom's dev effect-dispatch wrapper (dispatchEffectDev) catches every update-loop effect upstream, so Phase 1 callers of this hook will NOT observe invocations. Third-party effect libraries must not rely on this hook being called during Phase 1. Phase 2 wires this for off-loop dispatches (e.g., effects dispatched from Web Workers or post-mount lifecycle hooks) where @llui/dom's wrapper doesn't reach.

function _setEffectInterceptor(hook: EffectInterceptor): void

`asOnEffect()`

Adapt a handleEffects() chain (the (ctx) => void returned by .else()) to the signal-runtime onEffect shape: (effect, api) => cleanup. The signal runtime now hands onEffect a per-mount api.signal (an AbortSignal aborted exactly once, on THIS mount's dispose()). When present, this adapter passes that signal straight through to the chain: every mount owns a distinct signal, so the chain keys its per-mount registries off it and two concurrent mounts of one definition never interfere. Teardown is driven by the runtime aborting api.signal, so the returned cleanup is a no-op — the chain's own abort listener clears the mount's pending http / debounce / interval / websocket resources. We must NOT abort api.signal ourselves (it is the runtime's, shared with everything else on the mount). FALLBACK: when no api.signal is supplied (a bare unit test, or a non-signal caller), the adapter owns one AbortController per mount and the returned cleanup aborts it. It is (re)created lazily — never at factory-call time, since asOnEffect typically runs at module top-level where constructing an AbortController throws on Cloudflare Workers — and recreated once aborted so a re-mount of the same definition never inherits a dead signal. The cleanup is memoized per generation so it always targets the controller live at its dispatch. Usage: onEffect: asOnEffect(handleEffects<E, M>().use(…).else(…)).

function asOnEffect<E extends { type: string }, M>(chain: (ctx: EffectCtx<E, M>) => void): (effect: E, api: { send: (msg: M) => void; signal?: AbortSignal }) => () => void

`broadcast()`

function broadcast(channel: string, data: unknown): BroadcastEffect

`broadcastListen()`

function broadcastListen<M>(channel: string, onMessage: (data: unknown) => M): BroadcastListenEffect<M>

`buildRequest()`

Build the RequestInit (method + body + content-type headers) for an http effect, WITHOUT a signal. Shared by the live runHttp and the SSR resolveEffects so both derive identical requests. Callers add signal (and any timeout) themselves. @internal

function buildRequest(effect: HttpEffect): RequestInit

`cancel()`

export function cancel(token: string): CancelEffect
export function cancel(token: string, inner: BuiltinEffect): CancelReplaceEffect

`clipboardRead()`

function clipboardRead<M>(opts: {
  onSuccess: (text: string) => M
  onError: (error: string) => M
}): ClipboardReadEffect<M>

`clipboardWrite()`

function clipboardWrite(text: string): ClipboardWriteEffect

`debounce()`

function debounce(key: string, ms: number, inner: BuiltinEffect): DebounceEffect

`geolocation()`

function geolocation<M>(opts: {
  onSuccess: (position: { latitude: number; longitude: number; accuracy: number }) => M
  onError: (error: string) => M
  enableHighAccuracy?: boolean
}): GeolocationEffect<M>

`handleEffects()`

Batteries-included handler chain — handles every built-in effect out of the box. See {@link handleEffectsWith} for the tree-shakeable, hand-picked-runner form.

function handleEffects<E extends { type: string }, M = never>(): EffectChain<E, M>

`handleEffectsWith()`

Build a handler chain over an explicit set of runners. handleEffects() is this with the batteries-included {@link defaultRunners}; pass a hand-picked subset here to tree-shake unused runner code out of the bundle. Per-mount registries are keyed off each mount's lifecycle AbortSignal (a WeakMap so a torn-down mount's registry is collectible once its signal is unreachable). One registry is created lazily per distinct signal — i.e. per mount — and torn down exactly once when that signal aborts. Keying off the signal (rather than a chain-level closure) keeps two concurrent mounts of the same component isolated: disposing one never cancels the other's in-flight http / intervals / debounces / websockets.

function handleEffectsWith<E extends { type: string }, M = never>(runners: readonly Runner[]): EffectChain<E, M>

`http()`

function http<M>(opts: {
  url: string
  method?: string
  body?: unknown
  contentType?: string
  headers?: Record<string, string>
  timeout?: number
  responseType?: 'json' | 'text' | 'blob' | 'arrayBuffer'
  onSuccess: (data: unknown, headers: Headers) => M
  onError: (error: ApiError) => M
}): HttpEffect<M>

`httpStatusToApiError()`

function httpStatusToApiError(res: Response): Promise<ApiError>

`interval()`

function interval<M>(key: string, ms: number, msg: M): IntervalEffect

`log()`

Log to the console as an effect. Replaces the old core log effect.

function log(message: string, opts?: { level?: LogEffect['level']; data?: unknown }): LogEffect

`notification()`

function notification<M>(title: string, opts?: {
    body?: string
    icon?: string
    tag?: string
    onClick?: () => M
    onClose?: () => M
    onError?: () => M
  }): NotificationEffect<M>

`parseResponse()`

Parse a response body by explicit responseType, else auto-detect from the content-type header. Shared by runHttp and resolveEffects. @internal

function parseResponse(res: Response, responseType?: 'json' | 'text' | 'blob' | 'arrayBuffer'): Promise<unknown>

`race()`

function race(effects: BuiltinEffect[]): RaceEffect

`resolveEffects()`

Execute all HTTP effects from the effect list, apply responses to state via update(), return the final loaded state. Requests are built with the SAME buildRequest/parseResponse core the live http runner uses, so SSR pre-loading derives identical requests (real headers, content-type, pass-through bodies, responseType) and passes the response's real Headers to onSuccess. A rejected fetch (network failure / timeout) is mapped through the effect's onError rather than silently dropped, so SSR and the client converge on the same failure state.

function resolveEffects<S, M extends { type: string }, E extends { type: string }>(state: S, effects: E[], update: UpdateFn<S, M, E>, maxDepth = 3): Promise<S>

`retry()`

function retry(inner: HttpEffect, opts: { maxAttempts: number; delayMs: number }): RetryEffect

`sequence()`

function sequence(effects: BuiltinEffect[]): SequenceEffect

`storageGet()`

function storageGet<M>(key: string, onLoad: (value: unknown) => M, scope: StorageScope = 'local'): StorageGetEffect<M>

`storageLoad()`

Synchronous read from storage. Use at init time to seed state. Returns null on miss or invalid JSON.

function storageLoad<T = unknown>(key: string, scope: StorageScope = 'local'): T | null

`storageRemove()`

function storageRemove(key: string, scope: StorageScope = 'local'): StorageRemoveEffect

`storageSet()`

function storageSet(key: string, value: unknown, scope: StorageScope = 'local'): StorageSetEffect

`storageWatch()`

function storageWatch<M>(key: string, onChange: (value: unknown) => M, scope: StorageScope = 'local'): StorageWatchEffect<M>

`timeout()`

function timeout<M>(ms: number, msg: M): TimeoutEffect

`upload()`

function upload<M>(opts: {
  url: string
  method?: string
  body: FormData | Blob
  headers?: Record<string, string>
  timeout?: number
  onProgress: (loaded: number, total: number) => M
  onSuccess: (data: unknown, status: number) => M
  onError: (error: ApiError) => M
}): UploadEffect<M>

`websocket()`

function websocket<M>(opts: {
  url: string
  key: string
  protocols?: string[]
  onOpen?: () => M
  onMessage: (data: unknown) => M
  onClose?: (code: number, reason: string) => M
  onError?: () => M
}): WebSocketEffect<M>

`wsSend()`

function wsSend(key: string, data: unknown): WebSocketSendEffect

Types

`ApiError`

Standard API error type produced by the http() effect.

export type ApiError =
  | { kind: 'network'; message: string }
  | { kind: 'timeout' }
  | { kind: 'notfound' }
  | { kind: 'unauthorized' }
  | { kind: 'forbidden' }
  | { kind: 'ratelimit'; retryAfter?: number }
  | { kind: 'validation'; fields: Record<string, string[]> }
  | { kind: 'server'; status: number; message: string }

`Async`

Models the lifecycle of an async operation.

export type Async<T, E> =
  | { type: 'idle' }
  | { type: 'loading'; stale?: T }
  | { type: 'success'; data: T }
  | { type: 'failure'; error: E }

`Effect`

export type BuiltinEffect =
  | HttpEffect
  | CancelEffect
  | CancelReplaceEffect
  | DebounceEffect
  | TimeoutEffect
  | IntervalEffect
  | LogEffect
  | StorageSetEffect
  | StorageRemoveEffect
  | StorageGetEffect
  | StorageWatchEffect
  | BroadcastEffect
  | BroadcastListenEffect
  | SequenceEffect
  | RaceEffect
  | WebSocketEffect
  | WebSocketSendEffect
  | RetryEffect
  | UploadEffect
  | ClipboardReadEffect
  | ClipboardWriteEffect
  | NotificationEffect
  | GeolocationEffect

`EffectInterceptor`

export type EffectInterceptor = ((effect: unknown, id: string) => EffectInterceptorResult) | null

`EffectInterceptorResult`

Dev-only effect interceptor hook — consumed by @llui/mcp (via @llui/dom's devtools wiring) to implement effect mocking. Contract:

Default state is null — zero overhead when no interceptor is set.
Calling _setEffectInterceptor(null) clears the hook.
The hook receives the raw effect object and an opaque dispatch ID; it returns either { mocked: true, response } to short-circuit the real effect dispatch, or { mocked: false } to pass through. Phase 1 consumers rely on the pass-through path; the short-circuit path is exercised end-to-end through @llui/dom's effect-dispatch wrapper. This module only owns the null-safe set/get contract.

export type EffectInterceptorResult = { mocked: true; response: unknown } | { mocked: false }

`EffectPlugin`

Plugin handler — returns true if the effect was handled, false to pass through.

export type EffectPlugin<E, M> = (ctx: EffectCtx<E, M>) => boolean

`StorageScope`

export type StorageScope = 'local' | 'session'

Interfaces

`BroadcastEffect`

Post a message to a BroadcastChannel. Fire-and-forget.

export interface BroadcastEffect {
  type: 'broadcast'
  channel: string
  data: unknown
}

`BroadcastListenEffect`

Subscribe to a BroadcastChannel. Fires the message returned by onMessage(data) per incoming message.

export interface BroadcastListenEffect<M = unknown> {
  type: 'broadcast-listen'
  channel: string
  onMessage: (data: unknown) => M
}

`CancelEffect`

export interface CancelEffect {
  type: 'cancel'
  token: string
}

`CancelReplaceEffect`

export interface CancelReplaceEffect {
  type: 'cancel'
  token: string
  inner: BuiltinEffect
}

`ClipboardReadEffect`

export interface ClipboardReadEffect<M = unknown> {
  type: 'clipboard-read'
  onSuccess: (text: string) => M
  onError: (error: string) => M
}

`ClipboardWriteEffect`

export interface ClipboardWriteEffect {
  type: 'clipboard-write'
  text: string
}

`DebounceEffect`

export interface DebounceEffect {
  type: 'debounce'
  key: string
  ms: number
  inner: BuiltinEffect
}

`EffectCtx`

export interface EffectCtx<E, M> {
  effect: E
  send: (msg: M) => void
  signal: AbortSignal
}

`GeolocationEffect`

export interface GeolocationEffect<M = unknown> {
  type: 'geolocation'
  onSuccess: (position: { latitude: number; longitude: number; accuracy: number }) => M
  onError: (error: string) => M
  enableHighAccuracy?: boolean
}

`HttpEffect`

export interface HttpEffect<M = unknown> {
  type: 'http'
  url: string
  method?: string
  body?: unknown
  contentType?: string
  headers?: Record<string, string>
  timeout?: number
  responseType?: 'json' | 'text' | 'blob' | 'arrayBuffer'
  onSuccess: (data: unknown, headers: Headers) => M
  onError: (error: ApiError) => M
}

`IntervalEffect`

Fires msg every ms milliseconds. Cancel with cancel(key).

export interface IntervalEffect {
  type: 'interval'
  key: string
  ms: number
  msg: unknown
}

`LogEffect`

Write to the console as an effect (effects-as-data debug aid). The signal runtime intentionally does NOT special-case a log effect in core — it is just data handled here, like every other effect.

export interface LogEffect {
  type: 'log'
  message: string
  level?: 'log' | 'info' | 'warn' | 'error' | 'debug'
  data?: unknown
}

`NotificationEffect`

export interface NotificationEffect<M = unknown> {
  type: 'notification'
  title: string
  body?: string
  icon?: string
  tag?: string
  onClick?: () => M
  onClose?: () => M
  onError?: () => M
}

`RaceEffect`

export interface RaceEffect {
  type: 'race'
  effects: BuiltinEffect[]
}

`RetryEffect`

export interface RetryEffect {
  type: 'retry'
  /** Only `http` effects are retriable — retry re-issues the request on failure. */
  inner: HttpEffect
  maxAttempts: number
  delayMs: number
}

`Runner`

A single effect runner. types are the effect type discriminants this runner claims; run executes the effect; completesWithoutDispatch is the static signal used by sequence to advance past a fire-and-forget step immediately — a step that never calls send would otherwise stall the chain forever. run may RETURN a boolean to override completesWithoutDispatch on a per-call basis (only cancel needs this: bare cancel completes without dispatching, but cancel(token, inner) may dispatch via its inner effect). Returning undefined/void falls back to the static completesWithoutDispatch.

export interface Runner {
  readonly types: readonly string[]
  readonly completesWithoutDispatch: boolean
  run(effect: { type: string }, send: InternalSend, signal: AbortSignal, deps: Deps): boolean | void
}

`SequenceEffect`

export interface SequenceEffect {
  type: 'sequence'
  effects: BuiltinEffect[]
}

`StorageGetEffect`

Read a key from storage, dispatch the message returned by onLoad(value).

export interface StorageGetEffect<M = unknown> {
  type: 'storage-get'
  key: string
  onLoad: (value: unknown) => M
  scope: StorageScope
}

`StorageRemoveEffect`

Remove a key from storage. Fire-and-forget.

export interface StorageRemoveEffect {
  type: 'storage-remove'
  key: string
  scope: StorageScope
}

`StorageSetEffect`

Write a JSON value to localStorage/sessionStorage. Fire-and-forget.

export interface StorageSetEffect {
  type: 'storage-set'
  key: string
  value: unknown
  scope: StorageScope
}

`StorageWatchEffect`

Listen for changes to a storage key. Fires the message returned by onChange(value) on cross-tab writes.

export interface StorageWatchEffect<M = unknown> {
  type: 'storage-watch'
  key: string
  onChange: (value: unknown) => M
  scope: StorageScope
}

`TimeoutEffect`

Fires msg once, after ms milliseconds. Auto-cancels if the component unmounts.

export interface TimeoutEffect {
  type: 'timeout'
  ms: number
  msg: unknown
}

`UploadEffect`

export interface UploadEffect<M = unknown> {
  type: 'upload'
  url: string
  method?: string
  body: FormData | Blob
  headers?: Record<string, string>
  /** Abort the upload after this many milliseconds (wires `xhr.timeout`). */
  timeout?: number
  onProgress: (loaded: number, total: number) => M
  onSuccess: (data: unknown, status: number) => M
  onError: (error: ApiError) => M
}

`WebSocketEffect`

export interface WebSocketEffect<M = unknown> {
  type: 'websocket'
  url: string
  key: string
  protocols?: string[]
  onOpen?: () => M
  onMessage: (data: unknown) => M
  onClose?: (code: number, reason: string) => M
  onError?: () => M
}

`WebSocketSendEffect`

export interface WebSocketSendEffect {
  type: 'ws-send'
  key: string
  data: unknown
}

Constants

`defaultRunners`

Every built-in runner, in the original dispatch order.

const defaultRunners: readonly Runner[]

`delay`

Delay then dispatch a message — the effects-as-data form of setTimeout. This is the replacement for the old core delay effect: delay(ms, msg) is timeout(ms, msg) (fire msg once after ms; auto-cancels on unmount).

const delay