#  [](https://www.npmjs.com/package/@thi.ng/rstream)  [](https://mastodon.thi.ng/@toxi) > [!NOTE] > This is one of 205 standalone projects, maintained as part > of the [@thi.ng/umbrella](https://github.com/thi-ng/umbrella/) monorepo > and anti-framework. > > 🚀 Please help me to work full-time on these projects by [sponsoring me on > GitHub](https://github.com/sponsors/postspectacular). Thank you! ❤️ - [About](#about) - [Conceptual differences to RxJS](#conceptual-differences-to-rxjs) - [Status](#status) - [New features & breaking changes in 9.0.0](#new-features--breaking-changes-in-900) - [New features & breaking changes in 6.0.0](#new-features--breaking-changes-in-600) - [Support packages](#support-packages) - [Related packages](#related-packages) - [Installation](#installation) - [Dependencies](#dependencies) - [Usage examples](#usage-examples) - [API](#api) - [Common configuration options](#common-configuration-options) - [Stream creation](#stream-creation) - [Stream](#stream) - [IDeref support](#ideref-support) - [Subscription](#subscription) - [Other stream creation helpers](#other-stream-creation-helpers) - [Meta streams](#meta-streams) - [Stream merging](#stream-merging) - [Unordered merge from multiple inputs (dynamic add/remove)](#unordered-merge-from-multiple-inputs-dynamic-addremove) - [Synchronized merge and labeled tuple objects](#synchronized-merge-and-labeled-tuple-objects) - [Stream splitting](#stream-splitting) - [Topic based splitting](#topic-based-splitting) - [Splitting via predicate](#splitting-via-predicate) - [Side-chaining](#side-chaining) - [Input chunking / buffering, controlled by sidechain](#input-chunking--buffering-controlled-by-sidechain) - [Input toggling, controlled by sidechain](#input-toggling-controlled-by-sidechain) - [Input passthrough, controlled by sidechain](#input-passthrough-controlled-by-sidechain) - [Worker support](#worker-support) - [Parallel stream processing via workers](#parallel-stream-processing-via-workers) - [Stream processing via workers](#stream-processing-via-workers) - [Other subscription ops](#other-subscription-ops) - [Error handling](#error-handling) - [Authors](#authors) - [License](#license) ## About Reactive streams & subscription primitives for constructing dataflow graphs / pipelines. This library provides & uses three key building blocks for reactive programming: - **Stream sources**: event targets, iterables, timers, promises,watches, workers, manual-push... - **Subscriptions**: chained stream processors, each subscribable (one-tmany) itself - **Transducers**: stream transformers, either as individual subscription or to transform incoming values for a single subscription. See packages/transducers) for 100+ composable operators. - **Recursive teardown**: Whenever possible, and depending on configuration, unsubscriptions initiate cleanup and propagate to parent(s). - **Workers**: highly configurable, web worker integration for concurrent / parallel stream processing (fork-join, tunneled stream processing, etc.) ## Conceptual differences to RxJS (No value judgments implied - there's room for both approaches!) - Streams are not the same as Observables: I.e. stream sources are NOT (often just cannot) re-run for each new sub added. Only the first sub is guaranteed to receive **all** values. Subs added at a later time MIGHT not receive earlier emitted values, but only the most recent emitted and any future values - Every subscription supports any number of subscribers, which can be added/removed at any time - Depending on configuration options, every unsubscription recursively triggers upstream unsubscriptions (provided a parent has no other active child subscriptions) - Every subscription can have its own transducer transforming incoming values (possibly into multiple new ones) - Transducers can create streams themselves (only for `merge()` /`sync()`) - Transducers can cause early stream termination and subsequent unwinding for its parent and downstream subscriptions. - Values can be manually injected into the stream pipeline / graph at any point - Unhandled errors in a subscription will move the subscription into an error state and cause unsubscription from parent (if any). Unhandled errors in stream sources will cancel the stream. - _Much_ smaller API surface, since most common & custom operations can be solved via available transducers. Therefore there's less of a need to provide specialized functions (map / filter etc.) and gain more flexibility in terms of composing new operations. - IMHO less confusing naming / terminology (only streams (producers) & subscriptions (consumers)) ## Status **STABLE** - used in production [Search or submit any issues for this package](https://github.com/thi-ng/umbrella/issues?q=%5Brstream%5D+in%3Atitle) ### New features & breaking changes in 9.0.0 The `CloseMode` enum has been replaced with a more compact & simple string union type, see [docs](https://docs.thi.ng/umbrella/rstream/types/CloseMode.html) and [usage](#common-configuration-options). ### New features & breaking changes in 6.0.0 Completely revised & improved [error handling](#error-handling), stronger distinction between `.subscribe()` and `.transform()` methods & internal simplification of their implementations. 1. All error handlers now MUST return a boolean to indicate if the error was recoverable from or should put the subscription into the error state. See [error handling](#error-handling) for details. 2. The options given to `.transform()` and `.map()` can now include an `error` handler: ```ts // transform stream with given transducer(s) // and forward any errors to `handleError` (user defined fn) src.transform(xf1, xf2,..., { error: (e) => { ... } }); // or, also new, provide everything as single options object // (for this version, see note (1) below) src.transform({ xform: map(...), error: handleError }); ``` 3. The `.subscribe(sub, xform, opts)` signature has been removed and the `xform` (transducer) must now be given as part of the options object: ```ts import { reactive, trace } from "@thi.ng/rstream"; import { filter } from "@thi.ng/transducers"; const src = reactive(1); // old src.subscribe(trace("foo"), filter((x) => x < 10), { id: "child-sub" }); // new, see note (1) below src.subscribe(trace("foo"), { xform: filter((x) => x < 10), id: "child-sub" }); ``` 4. Added generics for [PubSub](#topic-based-splitting) topics, added `.transformTopic()` and updated signatures for `.subscribeTopic()`, both in similarity to above. ```ts import { pubsub } from "@thi.ng/rstream"; import { map } from "@thi.ng/transducers"; type Event = { id: string; value: any; }; const src = pubsub({ topic: (e) => e.id }); // transform topic stream with given transducer (see note (1) below) // and forward any errors to `handleError` (user defined fn) src.transformTopic("foo", map((e) => e.value), { error: handleError }) ``` **Notes:** - (1): If using multiple transducers, they must be pre-composed with [`comp()`](https://docs.thi.ng/umbrella/transducers/functions/comp.html). Other signatures of `.transform()` method support up to 4 transducers and composes them automatically. ## Support packages - [@thi.ng/rstream-csp](https://github.com/thi-ng/umbrella/tree/develop/packages/rstream-csp) - [@thi.ng/csp](https://github.com/thi-ng/umbrella/tree/develop/packages/csp) bridge module for [@thi.ng/rstream](https://github.com/thi-ng/umbrella/tree/develop/packages/rstream) - [@thi.ng/rstream-dot](https://github.com/thi-ng/umbrella/tree/develop/packages/rstream-dot) - Graphviz DOT conversion of [@thi.ng/rstream](https://github.com/thi-ng/umbrella/tree/develop/packages/rstream) dataflow graph topologies - [@thi.ng/rstream-gestures](https://github.com/thi-ng/umbrella/tree/develop/packages/rstream-gestures) - Unified mouse, mouse wheel & multi-touch event stream abstraction - [@thi.ng/rstream-graph](https://github.com/thi-ng/umbrella/tree/develop/packages/rstream-graph) - Declarative dataflow graph construction for [@thi.ng/rstream](https://github.com/thi-ng/umbrella/tree/develop/packages/rstream) - [@thi.ng/rstream-log](https://github.com/thi-ng/umbrella/tree/develop/packages/rstream-log) - Structured, multilevel & hierarchical loggers based on [@thi.ng/rstream](https://github.com/thi-ng/umbrella/tree/develop/packages/rstream) - [@thi.ng/rstream-log-file](https://github.com/thi-ng/umbrella/tree/develop/packages/rstream-log-file) - File output handler for structured, multilevel & hierarchical loggers based on [@thi.ng/rstream](https://github.com/thi-ng/umbrella/tree/develop/packages/rstream) - [@thi.ng/rstream-query](https://github.com/thi-ng/umbrella/tree/develop/packages/rstream-query) - [@thi.ng/rstream](https://github.com/thi-ng/umbrella/tree/develop/packages/rstream) based triple store & reactive query engine ## Related packages - [@thi.ng/atom](https://github.com/thi-ng/umbrella/tree/develop/packages/atom) - Mutable wrappers for nested immutable values with optional undo/redo history and transaction support - [@thi.ng/hdom](https://github.com/thi-ng/umbrella/tree/develop/packages/hdom) - Lightweight vanilla ES6 UI component trees with customizable branch-local behaviors - [@thi.ng/rdom](https://github.com/thi-ng/umbrella/tree/develop/packages/rdom) - Lightweight, reactive, VDOM-less UI/DOM components with async lifecycle and [@thi.ng/hiccup](https://github.com/thi-ng/umbrella/tree/develop/packages/hiccup) compatible - [@thi.ng/transducers](https://github.com/thi-ng/umbrella/tree/develop/packages/transducers) - Collection of ~170 lightweight, composable transducers, reducers, generators, iterators for functional data transformations ## Installation ```bash yarn add @thi.ng/rstream ``` ESM import: ```ts import * as rs from "@thi.ng/rstream"; ``` Browser ESM import: ```html ``` [JSDelivr documentation](https://www.jsdelivr.com/) For Node.js REPL: ```js const rs = await import("@thi.ng/rstream"); ``` Package sizes (brotli'd, pre-treeshake): ESM: 6.33 KB ## Dependencies - [@thi.ng/api](https://github.com/thi-ng/umbrella/tree/develop/packages/api) - [@thi.ng/arrays](https://github.com/thi-ng/umbrella/tree/develop/packages/arrays) - [@thi.ng/associative](https://github.com/thi-ng/umbrella/tree/develop/packages/associative) - [@thi.ng/atom](https://github.com/thi-ng/umbrella/tree/develop/packages/atom) - [@thi.ng/checks](https://github.com/thi-ng/umbrella/tree/develop/packages/checks) - [@thi.ng/errors](https://github.com/thi-ng/umbrella/tree/develop/packages/errors) - [@thi.ng/logger](https://github.com/thi-ng/umbrella/tree/develop/packages/logger) - [@thi.ng/transducers](https://github.com/thi-ng/umbrella/tree/develop/packages/transducers) Note: @thi.ng/api is in _most_ cases a type-only import (not used at runtime) ## Usage examples 56 projects in this repo's [/examples](https://github.com/thi-ng/umbrella/tree/develop/examples) directory are using this package: | Screenshot | Description | Live demo | Source | |:-------------------------------------------------------------------------------------------------------------------------------------|:--------------------------------------------------------------------------------------------------------|:----------------------------------------------------------|:---------------------------------------------------------------------------------------| | | Interactive image processing (adaptive threshold) | [Demo](https://demo.thi.ng/umbrella/adaptive-threshold/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/adaptive-threshold) | | | Large ASCII font text generator using @thi.ng/rdom | [Demo](https://demo.thi.ng/umbrella/big-font/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/big-font) | | | Figlet-style bitmap font creation with transducers | [Demo](https://demo.thi.ng/umbrella/bitmap-font/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/bitmap-font) | | | Interactive & reactive image blurhash generator | [Demo](https://demo.thi.ng/umbrella/blurhash/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/blurhash) | | | Canvas based dial widget | [Demo](https://demo.thi.ng/umbrella/canvas-dial/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/canvas-dial) | | | Self-modifying, animated typographic grid with emergent complex patterns | [Demo](https://demo.thi.ng/umbrella/canvas-recorder/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/canvas-recorder) | | | Tool to interactively compute & visualize color contrasts against WCAG threshold | [Demo](https://demo.thi.ng/umbrella/color-contrast/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/color-contrast) | | | Probabilistic color theme generator | [Demo](https://demo.thi.ng/umbrella/color-themes/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/color-themes) | | | Basic crypto-currency candle chart with multiple moving averages plots | [Demo](https://demo.thi.ng/umbrella/crypto-chart/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/crypto-chart) | | | Color palette generation via dominant color extraction from uploaded images | [Demo](https://demo.thi.ng/umbrella/dominant-colors/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/dominant-colors) | | | Interactive inverse FFT toy synth | [Demo](https://demo.thi.ng/umbrella/fft-synth/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/fft-synth) | | | Mouse gesture / stroke analysis, simplification, corner detection | [Demo](https://demo.thi.ng/umbrella/gesture-analysis/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/gesture-analysis) | | | Interactive pattern drawing demo using transducers | [Demo](https://demo.thi.ng/umbrella/hdom-canvas-draw/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/hdom-canvas-draw) | | | Various hdom-canvas shape drawing examples & SVG conversion / export | [Demo](https://demo.thi.ng/umbrella/hdom-canvas-shapes/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/hdom-canvas-shapes) | | | Canvas based Immediate Mode GUI components | [Demo](https://demo.thi.ng/umbrella/imgui/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/imgui) | | | Browser REPL for a Lispy S-expression based mini language | [Demo](https://demo.thi.ng/umbrella/lispy-repl/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/lispy-repl) | | | Worker based, interactive Mandelbrot visualization | [Demo](https://demo.thi.ng/umbrella/mandelbrot/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/mandelbrot) | | | Markdown to Hiccup to HTML parser / transformer | [Demo](https://demo.thi.ng/umbrella/markdown/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/markdown) | | | Mastodon API feed reader with support for different media types, fullscreen media modal, HTML rewriting | [Demo](https://demo.thi.ng/umbrella/mastodon-feed/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/mastodon-feed) | | | Basic rstream-gestures multi-touch demo | [Demo](https://demo.thi.ng/umbrella/multitouch/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/multitouch) | | | Parser grammar livecoding editor/playground & codegen | [Demo](https://demo.thi.ng/umbrella/parse-playground/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/parse-playground) | | | Interactive pixel sorting tool using thi.ng/color & thi.ng/pixel | [Demo](https://demo.thi.ng/umbrella/pixel-sorting/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/pixel-sorting) | | | RGB waveform image analysis | [Demo](https://demo.thi.ng/umbrella/pixel-waveform/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/pixel-waveform) | | | Live coding playground for 2D geometry generation using @thi.ng/pointfree-lang | [Demo](https://demo.thi.ng/umbrella/pointfree-geom/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/pointfree-geom) | | | Procedural stochastic text generation via custom DSL, parse grammar & AST transformation | [Demo](https://demo.thi.ng/umbrella/procedural-text/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/procedural-text) | | | Scroll-based, reactive, multi-param CSS animation basics | [Demo](https://demo.thi.ng/umbrella/ramp-scroll-anim/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/ramp-scroll-anim) | | | Demonstates various rdom usage patterns | [Demo](https://demo.thi.ng/umbrella/rdom-basics/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/rdom-basics) | | | Minimal rdom-canvas animation | [Demo](https://demo.thi.ng/umbrella/rdom-canvas-basics/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/rdom-canvas-basics) | | | Dynamically loaded images w/ preloader state | [Demo](https://demo.thi.ng/umbrella/rdom-delayed-update/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/rdom-delayed-update) | | | Basic usage of the declarative rdom-forms generator | [Demo](https://demo.thi.ng/umbrella/rdom-formgen/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/rdom-formgen) | | | rstream & transducer-based FSM for converting key event sequences into high-level commands | [Demo](https://demo.thi.ng/umbrella/rdom-key-sequences/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/rdom-key-sequences) | | | Basic usage of thi.ng/rdom keyed list component wrapper | [Demo](https://demo.thi.ng/umbrella/rdom-klist/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/rdom-klist) | | | rdom & hiccup-canvas interop test | [Demo](https://demo.thi.ng/umbrella/rdom-lissajous/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/rdom-lissajous) | | | Full umbrella repo doc string search w/ paginated results | [Demo](https://demo.thi.ng/umbrella/rdom-search-docs/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/rdom-search-docs) | | | rdom powered SVG graph with draggable nodes | [Demo](https://demo.thi.ng/umbrella/rdom-svg-nodes/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/rdom-svg-nodes) | | | Responsive image gallery with tag-based Jaccard similarity ranking | [Demo](https://demo.thi.ng/umbrella/related-images/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/related-images) | | | Generative audio synth offline renderer and WAV file export | [Demo](https://demo.thi.ng/umbrella/render-audio/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/render-audio) | | | Animated Voronoi diagram, cubic splines & SVG download | [Demo](https://demo.thi.ng/umbrella/rotating-voronoi/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/rotating-voronoi) | | | Minimal demo of using rstream constructs to form an interceptor-style event loop | [Demo](https://demo.thi.ng/umbrella/rstream-event-loop/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/rstream-event-loop) | | | Interactive grid generator, SVG generation & export, undo/redo support | [Demo](https://demo.thi.ng/umbrella/rstream-grid/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/rstream-grid) | | | rstream based UI updates & state handling | [Demo](https://demo.thi.ng/umbrella/rstream-hdom/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/rstream-hdom) | | | rstream based spreadsheet w/ S-expression formula DSL | [Demo](https://demo.thi.ng/umbrella/rstream-spreadsheet/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/rstream-spreadsheet) | | | Minimal rstream sync() example using rdom | [Demo](https://demo.thi.ng/umbrella/rstream-sync/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/rstream-sync) | | | Declarative component-based system with central rstream-based pubsub event bus | [Demo](https://demo.thi.ng/umbrella/rstream-system-bus/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/rstream-system-bus) | | | Fork-join worker-based raymarch renderer (JS/CPU only) | [Demo](https://demo.thi.ng/umbrella/shader-ast-workers/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/shader-ast-workers) | | | Fitting, transforming & plotting 10k data points per frame using SIMD | [Demo](https://demo.thi.ng/umbrella/simd-plot/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/simd-plot) | | | Responsive & reactively computed stacked column layout | [Demo](https://demo.thi.ng/umbrella/stacked-layout/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/stacked-layout) | | | SVG path parsing & dynamic resampling | [Demo](https://demo.thi.ng/umbrella/svg-resample/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/svg-resample) | | | hdom based slide deck viewer & slides from my ClojureX 2018 keynote | [Demo](https://demo.thi.ng/umbrella/talk-slides/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/talk-slides) | | | thi.ng/rdom & thi.ng/rstream based quiz to guess thi.ng package names | [Demo](https://demo.thi.ng/umbrella/thing-packages-quiz/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/thing-packages-quiz) | | | Multi-layer vectorization & dithering of bitmap images | [Demo](https://demo.thi.ng/umbrella/trace-bitmap/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/trace-bitmap) | | | Transducer & rstream based hdom UI updates | [Demo](https://demo.thi.ng/umbrella/transducers-hdom/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/transducers-hdom) | | | Interactive ridge-line plot | [Demo](https://demo.thi.ng/umbrella/viz-ridge-lines/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/viz-ridge-lines) | | | Interactive scatter & line plot of low-discrepancy samples | [Demo](https://demo.thi.ng/umbrella/viz-scatter-plot/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/viz-scatter-plot) | | | rdom & WebGL-based image channel editor | [Demo](https://demo.thi.ng/umbrella/webgl-channel-mixer/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/webgl-channel-mixer) | | | WebGL cube maps with async texture loading | [Demo](https://demo.thi.ng/umbrella/webgl-cubemap/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/webgl-cubemap) | ## API [Generated API docs](https://docs.thi.ng/umbrella/rstream/) ### Common configuration options Since version 3.0.0 all stream and subscription factory functions take an optional object of [common configuration options](https://docs.thi.ng/umbrella/rstream/interfaces/CommonOpts.html) with **at least** these keys (each optional): ```ts interface CommonOpts { /** * Internal ID associated with this stream. If omitted, an autogenerated ID * will be used. */ id: string; /** * If false or `"never"`, the stream stays active even if all inputs are * done. If true (default) or `"last"`, the stream closes when the last * input is done. If `"first"`, the instance closes when the first input is * done. * * @defaultValue "last" */ closeIn: CloseMode; /** * If false or `"never"`, the stream stays active once there are no more * subscribers. If true (default) or `"last"`, the stream closes when the * last subscriber has unsubscribed. If `"first"`, the instance closes when * the first subscriber disconnects. * * @defaultValue "last" */ closeOut: CloseMode; /** * If true (default), stream caches last received value and pushes it to new * subscriberswhen they subscribe. If false, calling `.deref()` on this * stream will always return `undefined`. * * @defaultValue true */ cache: boolean; } ``` ### Stream creation #### Stream Docs: [stream()](https://docs.thi.ng/umbrella/rstream/functions/stream-1.html) Creates a new `Stream` instance, optionally with given `StreamSource` function and / or ID. If a `src` function is provided, the function will be only called (with the `Stream` instance as single argument) once the first subscriber has attached to the stream. If the function returns another function, it will be used for cleanup purposes if the stream is cancelled, e.g. if the last subscriber has unsubscribed. Streams are intended as (primarily async) data sources in a dataflow graph and are the primary construct for the various `from*()` functions provided by the package. However, streams can also be triggered manually (from outside the stream), in which case the user should call `stream.next()` to cause value propagation. ```ts import { stream, trace } from "@thi.ng/rstream"; a = stream((s) => { s.next(1); s.next(2); s.done(); }); a.subscribe(trace("a")); // a 1 // a 2 // a done // as reactive value mechanism b = stream(); // or alternatively // b = subscription(); b.subscribe(trace("b1")); b.subscribe(trace("b2")); // external trigger b.next(42); // b1 42 // b2 42 ``` ### IDeref support `Stream` (like all other types of `Subscription`) implements the [@thi.ng/api `IDeref`](https://docs.thi.ng/umbrella/api/interfaces/IDeref.html) interface which provides read access to a stream's last received value. This is useful for various purposes, e.g. in combination with @thi.ng/hdom, which supports direct embedding of streams (i.e. their values) into UI components (and will be deref'd automatically). If the stream has not yet emitted a value or if the stream is already done, it will deref to `undefined`. Furthermore, all subscription types can be configured (via the `cache` option) to NOT retain their last emitted value, in which case `.deref()` will always return `undefined`. #### Subscription Docs: [subscription()](https://docs.thi.ng/umbrella/rstream/functions/subscription-1.html) Creates a new `Subscription` instance, the fundamental datatype & building block provided by this package (`Stream`s are `Subscription`s too). Subscriptions can be: - linked into directed graphs (if async, not necessarily DAGs) - transformed using transducers (incl. early termination) - can have any number of subscribers (optionally each w/ their own transducer) - recursively unsubscribe themselves from parent after their last subscriber unsubscribed - will go into a non-recoverable error state if NONE of the subscribers has an error handler itself - implement the @thi.ng/api `IDeref` interface ```ts import { subscription, trace } from "@thi.ng/rstream"; import { filter } from "@thi.ng/transducers"; // as reactive value mechanism (same as with stream() above) s = subscription(); s.subscribe(trace("s1")); s.subscribe(trace("s2"), filter((x) => x > 25)); // external trigger s.next(23); // s1 23 // (s2 doesn't receive value here due to its filter) s.next(42); // s2 42 // s1 42 ``` #### Other stream creation helpers - [reactive()](https://docs.thi.ng/umbrella/rstream/functions/reactive.html) - syntax sugar for `stream()` with initial value - [fromAtom()](https://docs.thi.ng/umbrella/rstream/functions/fromAtom.html) - streams from value changes in atoms/cursors - [fromChannel()](https://github.com/thi-ng/umbrella/tree/develop/packages/rstream-csp) - CSP channel to stream conversion - [fromEvent()](https://docs.thi.ng/umbrella/rstream/functions/fromEvent.html) - events - [fromDOMEvent()](https://docs.thi.ng/umbrella/rstream/functions/fromDOMEvent.html) - DOM events - [fromInterval()](https://docs.thi.ng/umbrella/rstream/functions/fromInterval.html) - interval based counters - [fromIterable()](https://docs.thi.ng/umbrella/rstream/functions/fromIterable.html) - arrays, iterators / generators (async & sync) - [fromNodeJS()](https://docs.thi.ng/umbrella/rstream/functions/fromNodeJS.html) - NodeJS stream adapter - [linesFromNodeJS()](https://docs.thi.ng/umbrella/rstream/functions/linesFromNodeJS.html) - NodeJS stream adapter - [fromObject()](https://docs.thi.ng/umbrella/rstream/functions/fromObject.html) - object property streams - [fromPromise()](https://docs.thi.ng/umbrella/rstream/functions/fromPromise.html) - single value stream from promise - [fromPromises()](https://docs.thi.ng/umbrella/rstream/functions/fromPromises.html) - results from multiple promise - [fromRAF()](https://docs.thi.ng/umbrella/rstream/functions/fromRAF.html) - requestAnimationFrame() counter (w/ node fallback) - [fromTuple()](https://docs.thi.ng/umbrella/rstream/functions/fromTuple.html) - tuple/vector per-component streams - [fromView()](https://docs.thi.ng/umbrella/rstream/functions/fromView.html) - derived view value changes (see [@thi.ng/atom](https://github.com/thi-ng/umbrella/tree/develop/packages/atom)) - [fromWorker()](https://docs.thi.ng/umbrella/rstream/functions/fromWorker.html) - messages received from worker - [toggle()](https://docs.thi.ng/umbrella/rstream/functions/toggle.html) - on/off switch-like stream - [trigger()](https://docs.thi.ng/umbrella/rstream/functions/trigger.html) - one-off events ### Meta streams Docs: [metaStream()](https://docs.thi.ng/umbrella/rstream/functions/metaStream-1.html) `MetaStream`s are streams of streams. A `MetaStream` is a subscription type which transforms each incoming value into a new stream, subscribes to it (via an hidden / internal subscription) and then only passes values from that stream to its own subscribers. If a new value is received, the meta stream first unsubscribes from the possibly still active stream created from the previous input, before creating and subscribing to the new stream. Hence this stream type is useful for cases where streams need to be dynamically and invisibly created & inserted into an existing dataflow topology without changing it, and with the guarantee that never more than one of these is active at the same time. Similar behavior (without the restriction in number) can be achieved using `merge()` (see further below). The user supplied `factory` function will be called for each incoming value and is responsible for creating the new stream instances. If the function returns `null` / `undefined`, no further action will be taken (acts like a `filter` transducer, i.e. the incoming value is simply ignored). ```ts import { metastream, fromIterable, trace } from "@thi.ng/rstream"; import { repeat } from "@thi.ng/transducers"; // transform each received odd number into a stream // producing 3 copies of that number in the metastream // even numbers are ignored a = metastream( (x) => (x & 1) ? fromIterable(repeat("odd: " + x, 3), { delay: 100 }) : null ); a.subscribe(trace()) a.next(23) // odd: 23 // odd: 23 // odd: 23 a.next(42) // not odd, ignored by meta factory fn a.next(43) // odd: 43 // odd: 43 // odd: 43 ``` The factory function does NOT need to create new streams, but too can merely return other existing streams, and so making the meta stream act like a switch / stream selector. If the meta stream is the only subscriber to these input streams, you'll need to use the `closeOut: "never"` option when creating the inputs. This keeps them alive and allows for dynamic switching between them. ```ts import { metastream, fromIterable, trace } from "@thi.ng/rstream"; import { repeat } from "@thi.ng/transducers"; // infinite inputs a = fromIterable( repeat("a"), { delay: 1000, closeOut: "never" } ); b = fromIterable( repeat("b"), { delay: 1000, closeOut: "never" } ); // stream selector / switch m = metaStream((x) => x ? a : b); m.subscribe(trace("meta from: ")); m.next(true); // meta from: a m.next(false); // meta from: b m.next(true); // meta from: a ``` ### Stream merging #### Unordered merge from multiple inputs (dynamic add/remove) Docs: [merge()](https://docs.thi.ng/umbrella/rstream/functions/merge.html)  Returns a new `StreamMerge` instance, a subscription type consuming inputs from multiple inputs and passing received values on to any subscribers. Input streams can be added and removed dynamically. By default, `StreamMerge` calls `done()` when the last active input is done, but this behavior can be overridden via the [`closeIn` option](https://docs.thi.ng/umbrella/rstream/interfaces/StreamMergeOpts.html#closeIn). ```ts import { merge, fromIterable, trace } from "@thi.ng/rstream"; merge({ // input streams w/ different frequencies src: [ fromIterable([1, 2, 3], { delay: 10 }), fromIterable([10, 20, 30], { delay: 21 }), fromIterable([100, 200, 300], { delay: 7 }) ] }).subscribe(trace()); // 100 // 1 // 200 // 10 // 2 // 300 // 3 // 20 // 30 ``` Use the [`labeled()` transducer](https://docs.thi.ng/umbrella/transducers/functions/labeled.html) for each input to create a stream of labeled values and track their provenance: ```ts import { merge, fromIterable, trace } from "@thi.ng/rstream"; import { labeled } from "@thi.ng/transducers"; merge({ src: [ fromIterable([1, 2, 3]).transform(labeled("a")), fromIterable([10, 20, 30]).transform(labeled("b")), ] }).subscribe(trace()); // ["a", 1] // ["b", 10] // ["a", 2] // ["b", 20] // ["a", 3] // ["b", 30] ``` See [StreamMergeOpts](https://docs.thi.ng/umbrella/rstream/interfaces/StreamMergeOpts.html) for further reference of the various behavior options. ##### Adding inputs automatically If the `StreamMerge` receives a `Subscription`-like value from any of its inputs, it will not be processed as usual, but instead will be added as new input to the merge and then automatically remove once that stream is exhausted. ```ts import { merge, stream, fromIterable, trace } from "@thi.ng/rstream"; import { repeat } from "@thi.ng/transducers"; // stream source w/ transducer mapping values to new streams a = stream().map((x) => fromIterable(repeat(x, 3))); // simple 1Hz counter b = fromInterval(1000).map((x) => "b" + x); merge({ src: [a, b] }).subscribe(trace()); // 0 // 1 // 2 // sent "a" will be transformed into stream via above transducer // and then auto-added as new input to the StreamMerge a.next("abc"); // abc // abc // abc // 3 // 4 ``` #### Synchronized merge and labeled tuple objects Docs: [sync()](https://docs.thi.ng/umbrella/rstream/functions/sync.html)  Similar to `StreamMerge` above, but with extra synchronization of inputs. Before emitting any new values, `StreamSync` collects values until at least one has been received from _all_ inputs. Once that's the case, the collected values are sent as labeled tuple object to downstream subscribers. Each value in the emitted tuple objects is stored under their input stream's ID. Only the last value received from each input is passed on. After the initial tuple has been emitted, you can choose from two possible behaviors: 1. Any future change in any input will produce a new result tuple. These tuples will retain the most recently read values from other inputs. This behavior is the default and illustrated in the above schematic. 2. If the `reset` option is `true`, every input will have to provide at least one new value again until another result tuple is produced. Any done inputs are automatically removed. By default, `StreamSync` calls `done()` when the last active input is done, but this behavior can be overridden via the [`closeIn` option](https://docs.thi.ng/umbrella/rstream/interfaces/StreamMergeOpts.html#closeIn). ```ts import { sync, stream, trace } from "@thi.ng/rstream"; const a = stream(); const b = stream(); s = sync({ src: { a, b } }).subscribe(trace("result: ")); a.next(1); b.next(2); // result: { a: 1, b: 2 } ``` Input streams can be added and removed dynamically and the emitted tuple size adjusts to the current number of inputs (the next time a value is received from any input). If the `reset` option is enabled, the last emitted tuple is allowed to be incomplete, by default. To only allow complete tuples, also set the `all` option to `false`. The synchronization is done via the [`partitionSync()`](https://docs.thi.ng/umbrella/transducers/functions/partitionSync-1.html) transducer from the [@thi.ng/transducers](https://github.com/thi-ng/umbrella/tree/develop/packages/transducers) package. See this function's docs for further details. See [StreamSyncOpts](https://docs.thi.ng/umbrella/rstream/interfaces/StreamSyncOpts.html) for further reference of the various behavior options. ### Stream splitting #### Topic based splitting Docs: [pubsub()](https://docs.thi.ng/umbrella/rstream/functions/pubsub-1.html)  Topic based stream splitter. Applies `topic` function to each received value and only forwards it to child subscriptions for returned topic. The actual topic (return value from `topic` fn) can be of any type, apart from `undefined`. Complex topics (e.g objects / arrays) are allowed and they're matched with registered topics using @thi.ng/equiv by default (but customizable via `equiv` option). Each topic can have any number of subscribers. If a transducer is specified for the `PubSub`, it is always applied prior to passing the input to the topic function. I.e. in this case the topic function will receive the transformed inputs. PubSub supports dynamic topic subscriptions and unsubscriptions via `subscribeTopic()` and `unsubscribeTopic()`. However, **the standard `subscribe()` / `unsubscribe()` methods are NOT supported** (since meaningless here) and will throw an error! `unsubscribe()` can only be called WITHOUT argument to unsubscribe the entire `PubSub` instance (incl. all topic subscriptions) from the parent stream. #### Splitting via predicate Docs: [bisect()](https://docs.thi.ng/umbrella/rstream/functions/bisect.html) Returns a new `PubSub` instance using given predicate `pred` as boolean topic function and `a` & `b` as subscribers for truthy (`a`) and falsy `b` values. ```ts import { bisect, fromIterable, trace } from "@thi.ng/rstream"; fromIterable([1, 2, 3, 4]).subscribe( bisect((x) => !!(x & 1), trace("odd"), trace("even")) ); // odd 1 // even 2 // odd 3 // even 4 // odd done // even done ``` If `a` or `b` need to be subscribed to directly, then `a` / `b` MUST be first created as `Subscription` (if not already) and a reference kept prior to calling `bisect()`. ```ts import { bisect, fromIterable, subscription, trace } from "@thi.ng/rstream"; const odd = subscription(); const even = subscription(); odd.subscribe(trace("odd")); odd.subscribe(trace("odd x10"), tx.map((x) => x * 10)); even.subscribe(trace("even")); fromIterable([1, 2, 3, 4]).subscribe(bisect((x) => !!(x & 1), odd, even)); // odd x10 10 // odd 1 // even 2 // odd x10 30 // odd 3 // even 4 // odd done // odd x10 done // even done ``` ### Side-chaining #### Input chunking / buffering, controlled by sidechain Docs: [sidechainPartition()](https://docs.thi.ng/umbrella/rstream/functions/sidechainPartition-1.html)  Buffers values from `src` until side chain fires, then emits buffer (unless empty) and repeats process until either input is done. By default, the value read from the side chain is ignored, however the optional predicate can be used to only trigger for specific values / conditions. ```ts import { merge, fromEvent, fromRAF, sidechainPartition, trace } from "@thi.ng/rstream"; // queue event processing to only execute during the // requestAnimationFrame cycle (RAF) sidechainPartition( // merge various event streams merge([ fromEvent(document, "mousemove"), fromEvent(document, "mousedown"), fromEvent(document, "mouseup") ]), // sidechain control stream fromRAF() ).subscribe(trace()); ``` Since v8.0.0 there's [`syncRAF()`](https://docs.thi.ng/umbrella/rstream/functions/syncRAF-1.html), which allows the above to be simplified to: ```ts import { merge, fromEvent, syncRAF, trace } from "@thi.ng/rstream"; syncRAF( merge([ fromEvent(document, "mousemove"), fromEvent(document, "mousedown"), fromEvent(document, "mouseup") ]) ).subscribe(trace()); ``` #### Input toggling, controlled by sidechain Docs: [sidechainToggle()](https://docs.thi.ng/umbrella/rstream/functions/sidechainToggle-1.html)  Filters values from input based on values received from side chain. By default, the value read from the side chain is ignored, however the optional predicate can be used to only trigger for specific values/conditions. Every time the predicate fn returns true, the filter will be toggled on/off. Whilst switched off, no input values will be forwarded. ```ts import { sidechainToggle, fromInterval, trace } from "@thi.ng/rstream"; // use slower interval stream to toggle faster main stream on/off sidechainToggle(fromInterval(500), fromInterval(1000)).subscribe(trace()); // 0 // 3 // 4 // 7 // 8 ... ``` #### Input passthrough, controlled by sidechain Docs: [sidechainTrigger()](https://docs.thi.ng/umbrella/rstream/functions/sidechainTrigger-1.html) Buffers the most recent value received and only forwards it downstream whenever a new control value is received from the sidechain. ```ts import { sidechainTrigger, reactive, stream, trace } from "@thi.ng/rstream"; const src = reactive("payload"); const side = stream(); sidechainTrigger(src, side).subscribe(trace("data:")); side.next(1); // data: payload // every time sidechain triggers side.next(1); // data: payload // only newest value will be buffered src.next("update #1"); src.next("update #2"); // ...until side chain triggers again side.next(1); // data: update #2 ``` ### Worker support #### Parallel stream processing via workers Docs: [forkJoin()](https://docs.thi.ng/umbrella/rstream/functions/forkJoin.html)  ##### worker.ts ```ts const $self: Worker = self; self.addEventListener("message", (e) => { const { buf, factor } = e.data; $self.postMessage(buf.map((x) => x * factor)); }); ``` ##### main.ts ```ts import { forkJoin, trace } from "@thi.ng/rstream"; const src = stream(); // fork worker jobs & re-join results forkJoin({ src: src, // worker job preparation // this function is called for each worker ID and the results // of that function are the messages sent to the workers... fork: (id, numWorkers, buf) => { const size = (buf.length / numWorkers) | 0; return { buf: id < numWorkers - 1 ? buf.slice(id * size, (id + 1) * size) : buf.slice(id * size), factor: id * 10 }; }, // re-join worker results join: (parts) => Array.prototype.concat.apply([], parts), // worker script worker: "./worker.js", // default: navigator.hardwareConcurrency numWorkers: 4 }).subscribe(trace("results")); src.next(new Array(16).fill(1)); // result: [0, 0, 0, 0, 10, 10, 10, 10, 20, 20, 20, 20, 30, 30, 30, 30] ``` #### Stream processing via workers Docs: [tunnel()](https://docs.thi.ng/umbrella/rstream/functions/tunnel-1.html) Delegate stream value processing to workers and pass on their responses to downstream subscriptions. Supports multiple worker instances and worker termination / restart for each new stream value received. Docs: [postWorker()](https://docs.thi.ng/umbrella/rstream/functions/postWorker.html) Send values to workers (incl. optional (inline) worker instantiation) Docs: [fromWorker()](https://docs.thi.ng/umbrella/rstream/functions/fromWorker.html) Create value stream from worker messages. ### Other subscription ops - [debounce](https://docs.thi.ng/umbrella/rstream/functions/debounce.html): ignore high frequency interim values - [resolve](https://docs.thi.ng/umbrella/rstream/functions/resolve.html): resolve on-stream promises - [trace](https://docs.thi.ng/umbrella/rstream/functions/trace.html): debug helper - [transduce](https://docs.thi.ng/umbrella/rstream/functions/transduce.html): transduce or just reduce an entire stream into a promise - [tween](https://docs.thi.ng/umbrella/rstream/functions/tween.html): stream interpolation ### Error handling **Detailed information, discussion & diagrams about the new error handling can be found in [this issue](https://github.com/thi-ng/umbrella/issues/281)** The `ISubscriber` interface supports optional error handlers which will be called if code in the `next()` or `done()` handlers throws an error. If no error handler is defined for a subscriber, the wrapping `Subscription`'s own error handler will be called, which _might_ put this subscription into an error state and stop it from receiving new values. ```ts import { subscription, State } from "@thi.ng/rstream"; src = subscription({ next(x) { throw x; } }); // triggers error, caught by subscription wrapper src.next(1); // sub-0 unhandled error: 1 src.getState() === State.ERROR // true // no error, but also inputs won't be received/processed either src.next(2) // another sub with error handler & indicating error could be handled src = subscription({ next(x) { throw x; }, error(x) { console.warn("eeek", x); return true; } }); // error caught by given handler src.next(1) // eeek 1 // sub still usable, no error src.getState() !== State.ERROR // true // further inputs still accepted src.next(2) // eeek 2 ``` ## Authors - [Karsten Schmidt](https://thi.ng) (Main author) - [André Wachter](https://github.com/andrew8er) - [Gavin Cannizzaro](https://github.com/gavinpc-mindgrub) If this project contributes to an academic publication, please cite it as: ```bibtex @misc{thing-rstream, title = "@thi.ng/rstream", author = "Karsten Schmidt and others", note = "https://thi.ng/rstream", year = 2017 } ``` ## License © 2017 - 2025 Karsten Schmidt // Apache License 2.0