@thi.ng/hdom
Advanced tools
This project is part of the @thi.ng/umbrella monorepo.
Lightweight reactive DOM components & VDOM-ish implementation using only vanilla JS data structures (arrays, objects with life cycle functions, closures, iterators), based on @thi.ng/hiccup.
serialize()) and then "hydrating" listeners and
components with life cycle methodsstyle attribshdom is very flexible and supports different workflows and means to update a DOM...
In addition to the descriptions in this file, further information and examples are available in the wiki.
Also see the work-in-progress ADRs for component configuration.
import * as hdom from "@thi.ng/hdom";
// stateless component w/ params
// the first arg is an auto-injected context object
// (not used here, see `hdom-context-basics` example for details)
const greeter = (_, name) => ["h1.title", "hello ", name];
// component w/ local state
const counter = (i = 0) => {
return () => ["button", { onclick: () => (i++) }, `clicks: ${i}`];
};
const app = () => {
// initialization steps
// ...
// root component is just a static array
return ["div#app", [greeter, "world"], counter(), counter(100)];
};
// start update loop (browser only, see diagram below)
hdom.start(app(), { root: document.body });
// alternatively apply DOM tree only once
// (stateful components won't update though)
hdom.createDOM(document.body, hdom.normalizeTree(app()));
Live demo | standalone example
Alternatively, use the same component function for browser or server
side HTML serialization (Note: does not emit attributes w/ functions as
values, e.g. a button's onclick attrib).
import { serialize } from "@thi.ng/hiccup";
console.log(serialize(app()));
// <div id="app"><h1 class="title">hello world</h1><button>clicks: 0</button><button>clicks: 100</button></div>
This example uses the @thi.ng/transducers-hdom support library to perform reactive DOM updates (instead of regular diffing via RAF).
import * as rs from "@thi.ng/rstream/stream";
import * as tx from "@thi.ng/rstream/transducers";
import { updateDOM } from "@thi.ng/rstream/transducers-hdom";
// root component function
const app = ({ ticks, clicks }) =>
["div",
`${ticks} ticks & `,
["a",
{ href: "#", onclick: () => clickStream.next(0)},
`${clicks} clicks`]
];
// click stream (click counter)
const clickStream = rs.stream().transform(tx.scan(tx.count(-1)));
// stream combinator
// waits until all inputs have produced at least one value,
// then updates whenever any input has changed
sync({
// streams to synchronize
src: {
ticks: rs.fromInterval(1000),
clicks: clickStream,
},
}).transform(
// transform tuple into hdom component
tx.map(app),
// apply hdom tree to real DOM
updateDOM({ root: document.body })
);
// kick off
clickStream.next(0);
Live demo | standalone example
The actual DOM update is based on the minimal edit set of the recursive difference between the old and new DOM trees (both expressed as nested JS arrays). Components can be defined as static arrays, closures or objects with life cycle methods (init, render, release).
The syntax is inspired by Clojure's Hiccup and Reagent projects, however the latter is a wrapper around React, whereas this library is standalone, more low-level & less opinionated.
Since this package is purely dealing with the translation of DOM trees, any form of state / event handling or routing required by a full app is out of scope. These features are provided by the following packages and can be used in a mix & match manner:
A currently small (but growing) number of reusable components are provided by these packages:
The overall "API" is stable, but there's further work planned on generalizing the approach beyond standard browser DOM use cases. The project has been used for several projects in production since 2016.
yarn add @thi.ng/hdom
Use the customizable create-hdom-app project generator to create a pre-configured app skeleton using @thi.ng/atom, @thi.ng/hdom, @thi.ng/interceptors & @thi.ng/router:
yarn create hdom-app my-app
cd my-app
yarn install
yarn start
Even though the overall approach should be obvious from the code examples in this document, it's recommended to first study the @thi.ng/hiccup reference to learn about the basics of the approach and syntax used. Both projects started in early 2016, have somewhat evolved independently, however should be considered complementary.
start(tree: any, opts?: Partial<HDOMOpts>): () => anyMain user function of this package. For most use cases, this function
should be the only one required in user code. It takes a parent DOM
element (or ID), hiccup tree (array, function or component object w/
life cycle methods) and an optional arbitrary context object. Starts RAF
update loop, in each iteration first normalizing given tree, then
computing diff to previous frame's tree and applying any changes to the
real DOM. The optional context arg can be used for passing global
config data or state down into the hiccup component tree. Any embedded
component function in the tree will receive this context object as first
argument, as will life cycle methods in component objects. See context
description further below.
Selective updates: No updates will be applied if the given hiccup
tree is undefined or null or a root component function returns no
value. This way a given root component function can do some state
handling of its own and implement fail-fast checks to determine no DOM
updates are necessary, saving effort re-creating a new hiccup tree and
request skipping DOM updates via this function. In this case, the
previous DOM tree is kept around until the root function returns a tree
again, which then is diffed and applied against the previous tree kept
as usual. Any number of frames may be skipped this way.
Important: Unless the hydrate option is enabled, the parent
element given is assumed to have NO children at the time when start()
is called. Since hdom does NOT track the real DOM, the resulting changes
will result in potentially undefined behavior if the parent element
wasn't empty. Likewise, if hydrate is enabled, it is assumed that an
equivalent DOM (minus listeners) already exists (i.e. generated via SSR)
when start() is called. Any other discrepancies between the
pre-existing DOM and the hdom trees will cause undefined behavior.
Returns a function, which when called, immediately cancels the update loop.
normalizeTree(tree: any, ctx?: any): anyCalling this function is a prerequisite before passing a component tree
to diffElement. Recursively expands given hiccup component tree into
its canonical form by:
div#id.foo.bar)render life cycle method on component objects and using
resultderef() on elements implementing IDeref interface and
using returned result.toString() on any other non-component value x and by
default wrapping it in ["span", x]. The only exceptions to this are:
option, textarea and SVG text elements, for which spans are
always skipped.Additionally, unless keys is set to false, an unique key attribute
is created for each node in the tree. This attribute is used by
diffElement to determine if a changed node can be patched or will need
to be replaced/removed. The key values are defined by the path array
arg.
For normal usage only the first 2 args should be specified and the rest kept at their defaults.
diffElement(parent: Element, prev: any, curr: any): voidTakes a DOM root element and two hiccup trees, prev and curr.
Recursively computes diff between both trees and applies any necessary
changes to reflect curr tree in real DOM.
For newly added components, calls init with created DOM element (plus
user provided context and any other args) for any components with init
life cycle method. Likewise, calls release on components with
release method when the DOM element is removed.
Important: The actual DOM element/subtree given is assumed to
exactly represent the state of the prev tree. Since this function does
NOT track the real DOM at all, the resulting changes will result in
potentially undefined behavior if there're discrepancies.
createDOM(parent: Element, tag: any, insert?: number): anyCreates an actual DOM tree from given hiccup component and parent
element. Calls init with created element (user provided context and
other args) for any components with init life cycle method. Returns
created root element(s) - usually only a single one, but can be an array
of elements, if the provided tree is an iterable. Creates DOM text nodes
for non-component values. Returns parent if tree is null or
undefined.
hydrateDOM(parent: Element, tag: any)Takes a DOM root element and normalized hdom tree, then walks tree and initializes any event listeners and components with lifecycle init methods. Assumes that an equivalent DOM (minus listeners) already exists (e.g. generated via SSR) when called. Any other discrepancies between the pre-existing DOM and the hdom tree will cause undefined behavior.
Since v3.0.0 hdom offers support for an arbitrary "context" object
passed to start(), and then automatically injected as argument to
all embedded component functions anywhere in the tree. This avoids
having to manually pass down configuration data into each sub-component
and so can simplify certain use cases, e.g. event dispatch, style /
theme information, global state etc.
import { start } from "@thi.ng/hdom";
import { Event, EventBus } from "@thi.ng/interceptors";
// (optional) type aliases to better illustrate demo context structure
type AppContext = {
bus: EventBus,
ui: { link: string, list: string }
};
type LinkSpec = [Event, any];
// user defined context object
// should include whatever config is required by your components
const ctx: AppContext = {
// event processor from @thi.ng/interceptors
bus: new EventBus(),
// component styling (using Tachyons CSS)
ui: {
link: "fw7 blue link dim pointer",
list: "list center tc"
}
};
// link component with `onclick` handler, which dispatches `evt`
// on EventBus obtained from context
// `ctx` arg is automatically provided when component is called
const eventLink = (ctx: AppContext, evt: Event, ...body: any[]) =>
["a",
{
class: ctx.ui.link,
onclick: () => ctx.bus.dispatch(evt),
},
...body];
// list component wrapper for links
const linkList = (ctx: AppContext, ...links: LinkSpec[]) =>
["ul", { class: ctx.ui.list },
links.map((l) => ["li", [eventLink, ...l]])];
// root component
// i.e. creates list of of provided dummy event link specs
const root = [
linkList,
[["handle-login"], "Login"],
[["external-link", "http://thi.ng"], "thi.ng"],
];
// start hdom update loop
start(root, { ctx });
Most components can be succinctly expressed via vanilla JS functions, though for some use cases we need to get a handle on the actual underlying DOM element and can only fully initialize the component once it's been mounted etc. For those cases components can be specified as classes or plain objects implementing the following interface:
interface ILifecycle {
/**
* Component init method. Called with the actual DOM element,
* hdom user context and any other args when the component is
* first used, but **after** `render()` has been called once already.
*/
init?(el: Element, ctx: any, ...args: any[]);
/**
* Returns the hdom tree of this component.
* Note: Always will be called first (prior to `init`/`release`)
* to obtain the actual component definition used for diffing.
* Therefore might have to include checks if any local state
* has already been initialized via `init`. This is the only
* mandatory method which MUST be implemented.
*
* `render` is executed before `init` because `normalizeTree()`
* must obtain the component's hdom tree first before it can
* determine if an `init` is necessary. `init` itself will be
* called from `diffElement` (or `createDOM`) in a later
* phase of processing.
*/
render(ctx: any, ...args: any[]): any;
/**
* Called when the underlying DOM of this component is removed
* (or replaced). Intended for cleanup tasks.
*/
release?(ctx: any, ...args: any[]);
}
When the component is first used the order of execution is: render ->
init. The release method is only called when the component has been
removed / replaced (basically if it's not present in the new tree
anymore). release should NOT manually call release on any children,
since that's already handled by diffElement().
The rest ...args provided are sourced from the component call site as
this simple example demonstrates:
// wrap in closure to allow multiple instances
const canvas = () => {
return {
init: (el, ctx, { width, height }, msg, color = "red") => {
const c = el.getContext("2d");
c.fillStyle = color;
c.fillRect(0, 0, width, height);
c.fillStyle = "white";
c.textAlign = "center";
c.fillText(msg, width / 2, height / 2);
},
render: (ctx, attribs) => ["canvas", attribs],
};
};
// usage scenario #1: static component
// inline initialization is okay here...
start(
[canvas(), { width: 100, height: 100 }, "Hello world"],
{ root: document.body }
);
// usage scenario #2: dynamic component
// in this example, the root component itself is given as function, which
// is evaluated each frame
// since `canvas()` is a higher order component it too produces a new instance
// with each call. therefore the canvas instance(s) need to be created beforehand
const app = () => {
// pre-instantiate canvases
let c1 = canvas();
let c2 = canvas();
// return root component function
return () => ["div",
// some dynamic other content
["p", new Date().toString()],
// use canvas instances
[c1, { width: 100, height: 100 }, "Hello world"],
[c2, { width: 100, height: 100 }, "Goodbye world", "blue"]
];
};
start(app(), { root: document.body });
Most of the 25 examples included in this repo are using this package in one way or another. Please check them out to learn more. Each is heavily commented, incl. best practice notes.
Non-exhaustive list:
This is a preview of the upcoming @thi.ng/estuary package:
Based on the create-hdom-app project scaffolding, this is one of the
more advanced demos, combining functionality of several other @thi.ng
packages.
Devcards style BMI calculator(s) with basic SVG viz.
A fully documented, obligatory todo list app with undo / redo.
A stress test benchmark is here: /examples/benchmark
Based on user feedback collected via Twitter, performance should be more than acceptable for even quite demanding UIs. In the 192 / 256 cells configurations this stress test causes approx. 600 / 800 DOM every single frame, very unlikely for a typical web app. In Chrome 68 on a MBP2016 this still runs at a stable 60fps (192 cells) / 37fps (256 cells). Both FPS readings based the 50 frame SMA.
© 2016 - 2018 Karsten Schmidt // Apache Software License 2.0
FAQs
Lightweight vanilla ES6 UI component trees with customizable branch-local behaviors
The npm package @thi.ng/hdom receives a total of 209 weekly downloads. As such, @thi.ng/hdom popularity was classified as not popular.
We found that @thi.ng/hdom demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 0 open source maintainers collaborating on the project.
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