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This project is part of the @thi.ng/umbrella monorepo.


Transducer based UI updater for @thi.ng/hdom. This is a support package for @thi.ng/transducers.

This package provides a single updateDOM function, a side-effecting & stateful transducer which receives @thi.ng/hdom component trees, diffs each against the previous value and applies any required changes to the browser DOM, starting at given root element. By default, incoming values are first normalized using @thi.ng/hdom's normalizeTree() function. See hdom's start() function for more details.

If the hydrate option is given, the first received tree is only used to inject event listeners and initialize components with lifecycle init() methods and expects an otherwise identical pre-existing DOM. All succeeding trees are diffed then as usual.

This transducer is primarily intended for @thi.ng/rstream-based dataflow graphs, where it can be used as final leaf subscription / stream transformer to reflect UI changes back to the user, without using the usual RAF update loop used by @thi.ng/hdom by default. In this setup, DOM updates will only be performed if the stream this transducer is attached to receives new values (i.e. hdom component trees).

Please also see the following hdom references for further details:


STABLE - used in production

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Related packages

  • @thi.ng/hdom - Lightweight vanilla ES6 UI component trees with customizable branch-local behaviors
  • @thi.ng/interceptors - Interceptor based event bus, side effect & immutable state handling
  • @thi.ng/rstream - Reactive streams & subscription primitives for constructing dataflow graphs / pipelines


yarn add @thi.ng/transducers-hdom

ES module import:

<script type="module" src="https://cdn.skypack.dev/@thi.ng/transducers-hdom"></script>

Skypack documentation

For Node.js REPL:

const transducersHdom = await import("@thi.ng/transducers-hdom");

Package sizes (brotli'd, pre-treeshake): ESM: 272 bytes


Usage examples

Several demos in this repo's /examples directory are using this package.

A selection:

Screenshot Description Live demo Source
Interactive image processing (adaptive threshold) Demo Source
Figlet-style bitmap font creation with transducers Demo Source
Canvas based dial widget Demo Source
Basic crypto-currency candle chart with multiple moving averages plots Demo Source
Interactive inverse FFT toy synth Demo Source
Doodle w/ K-nearest neighbor search result visualization Demo Source
K-nearest neighbor search in an hash grid Demo Source
Mouse gesture / stroke analysis, simplification, corner detection Demo Source
Interactive pattern drawing demo using transducers Demo Source
Various hdom-canvas shape drawing examples & SVG conversion / export Demo Source
Isolated, component-local DOM updates Demo Source
Canvas based Immediate Mode GUI components Demo Source
Worker based, interactive Mandelbrot visualization Demo Source
Markdown to Hiccup to HTML parser / transformer Demo Source
Basic rstream-gestures multi-touch demo Demo Source
Polygon to cubic curve conversion & visualization Demo Source
Animated Voronoi diagram, cubic splines & SVG download Demo Source
Minimal demo of using rstream constructs to form an interceptor-style event loop Demo Source
rstream based UI updates & state handling Demo Source
rstream based spreadsheet w/ S-expression formula DSL Demo Source
hdom based slide deck viewer & slides from my ClojureX 2018 keynote Demo Source
Transducer & rstream based hdom UI updates Demo Source


Generated API docs

Code for the above linked transducers-hdom example...

import * as rs from "@thi.ng/rstream";
import * as tx from "@thi.ng/transducers";
import { updateDOM } from "@thi.ng/transducers-hdom";

// root component function
const app = ({ ticks, clicks }) =>
        `${ticks} ticks and `,
            { href: "#", onclick: () => clickStream.next(0) },
            `${clicks} clicks`]

// click stream (click counter)
const clickStream = new rs.Stream().transform(tx.scan(tx.count(-1)));

// stream combinator
    src: {
        ticks: rs.fromInterval(1000),
        clicks: clickStream,
    reset: false,
    // transform into hdom component
    // apply as DOM
    updateDOM({ root: document.body })

// kick off


If this project contributes to an academic publication, please cite it as:

  title = "@thi.ng/transducers-hdom",
  author = "Karsten Schmidt",
  note = "https://thi.ng/transducers-hdom",
  year = 2018


© 2018 - 2023 Karsten Schmidt // Apache License 2.0


npm i @thi.ng/transducers-hdom

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