hyper-arrow

super tiny front-end UI library, for educational purposes

• ~4.5KB minified
• ZERO dependencies
• No building steps, easy use via <script module="type"> tag in plain HTML
• Proxy-based reactivity, like reactive in Vue 3 or makeAutoObservable in MobX
• No templates or JSX. Tag functions div, button and etc. work like h in hyperscript or h in Vue 3
• => arrow functions within tag functions provide reactivity, which is how the name comes ;)
• Smart and performant element children inserting, removing, swapping and updating, if all children has unique id attributes

Get started

// @ts-nocheck
import { mount, reactive, tags } from '../../hyper-arrow.js'

class Model {
  input = ''
  list = []
  add() {
    this.list.push(this.input)
    this.input = ''
  }
  clear() {
    this.list = []
  }
}

// create a reactive object
const model = reactive(new Model())

// design your view with nested HTML tag functions
const { button, div, input, li, ul } = tags.html

const view = div(
  // element properties in the first parameter
  {
    id: 'container-id',
    class: 'container-class',
    style: 'padding: 4px;',
  },
  // children in the rest parameters
  div({ style: 'margin: 4px' }, 'hyper-arrow demo'),
  input({
    type: 'text',
    // arrow functions make properties reactive
    value: () => model.input,
    class: () => (model.input ? 'class3' : 'class4'),
    // your can set inline styles here with prefix '$'
    $margin: '4px',
    // again, arrow function for reactive style
    $color: () => (model.input.length > 5 ? 'red' : 'black'),
    // event listeners with prefix 'on'
    onInput(event) {
      model.input = event.target.value
    },
    onKeydown(event) {
      if (event.code === 'Enter') model.add()
    },
  }),
  button(
    {
      type: 'button',
      style: 'margin: 4px',
      onClick() {
        model.add()
      },
    },
    'add',
  ),
  // can also using 'innerText' to set text as single child
  // just like `el.innerText = 'xxx'` in DOM API
  button({
    type: 'button',
    innerText: 'clear all',
    style: () => 'margin: 4px;',
    onClick() {
      model.clear()
    },
  }),
  // element properties can be omitted, if none exists
  ul(
    // children can also be an arrow function, also reactive
    () => model.list.map((item) => li(item)),
  ),
)

// mount your view to the page and go!
mount('#app', view)

model.input = 'aaa'
model.add()
model.input = 'bbb'
model.add()

It will create the following DOM tree with proper dynamic behaviors:

<div id="container-id" class="container-class" style="padding: 4px;">
  <div style="margin: 4px;">hyper-arrow demo</div>
  <input type="text" class="class4" style="margin: 4px; color: black;" />
  <button type="button" style="margin: 4px;">add</button>
  <button type="button" style="margin: 4px;">clear all</button>
  <ul>
    <li>aaa</li>
    <li>bbb</li>
  </ul>
</div>

See src/examples for more.

Basic API

reactive(object)

Create a reactive proxy for any object, and then it can be used in tag functions.

tags

All HTML tag functions are in tags.html. tags.svg contains SVG tag functions, and tags.mathml contains MathML tag functions.

import { mount, reactive, tags } from '../../hyper-arrow.js'

const { div, button } = tags.html
const { svg, circle } = tags.svg
const { math, mi, mn, mfrac } = tags.mathml

const model = reactive({ number: 10 })

// children can be an array, instead of being the rest parameters
const view = div({ id: 'root' }, [
  button({
    innerText: 'increase',
    onClick() {
      model.number++
    },
  }),
  // if you have single-line props, then children as array formats better
  svg({ stroke: 'red', fill: 'lightyellow' }, [
    circle({ cx: '50', cy: '50', r: () => model.number.toString() }),
  ]),
  // same here, children in array
  math({ display: 'block' }, [
    // here children are not in array. writes easier and looks better
    mfrac(
      mi('x'),
      mn(() => model.number.toString()),
    ),
  ]),
])

mount('#app', view)

It generates the DOM tree:

<div id="root">
  <button>increase</button>
  <svg stroke="red" fill="lightyellow">
    <circle cx="50" cy="50" r="10"></circle>
  </svg>
  <math display="block">
    <mfrac><mi>x</mi><mn>10</mn></mfrac>
  </math>
</div>

mount(element_selector, view, [options])

Mount the view onto DOM. Examples already shown above. See below for details of optional options

Advanced API

UID_ATTR_NAME

mount can accept an optional third parameter options for extra configuration.

[UID_ATTR_NAME] is a unique symbol key in mount's options. It adds unique HTML attributes to all DOM elements created by mount in order to identify themselves.

import { mount, tags, UID_ATTR_NAME } from '../../hyper-arrow.js'

const { div } = tags.html

const view = div(div('a'), div('b'), div(div('c'), div('d')), div('e'))

mount('#app', view, { [UID_ATTR_NAME]: 'uid' })

will generate:

<div uid="0">
  <div uid="1">a</div>
  <div uid="2">b</div>
  <div uid="3">
    <div uid="4">c</div>
    <div uid="5">d</div>
  </div>
  <div uid="6">e</div>
</div>

This is useful, for example, when checking if the parent element, when doing smart children updating or caching, is reusing elements correctly instead of recreating new ones (see below).

CACHE_REMOVED_CHILDREN

A unique symbol key that allows allow a parent DOM element to cache all it's removed children elements, so instead of creating new children, it can reuse the cached ones when needed, as long as the children's id attributes match.

import {
  CACHE_REMOVED_CHILDREN,
  mount,
  reactive,
  tags,
  UID_ATTR_NAME,
} from '../../hyper-arrow.js'

const { div, button, ul, li } = tags.html

const model = reactive({ list: ['0', '1'] })

const view = div(
  button({
    innerText: 'change',
    onClick() {
      const length = Math.floor(Math.random() * 10)
      model.list = Array.from({ length }, (_, i) => i.toString())
    },
  }),
  // allows cache, with 100 as max cache size
  ul({ id: 'list', [CACHE_REMOVED_CHILDREN]: 100 }, () =>
    model.list.map((item) => li({ id: () => item }, item.toString())),
  ),
)

mount('#app', view, { [UID_ATTR_NAME]: 'uid' })

In the dev tool you can see that, when the list changes, the uid attributes of li elements remain the same. That shows ul is reusing old removed lis.

ON_CREATE

A unique symbol key to create a special "onCreate" event handler on a DOM element.

import { mount, ON_CREATE, tags } from '../../hyper-arrow.js'

const { input } = tags.html

mount(
  '#app',
  input({
    value: 'hello world',
    [ON_CREATE](el) {
      requestAnimationFrame(() => {
        el.focus()
        setTimeout(() => {
          el.select()
        }, 1000)
      })
    },
  }),
)

The created DOM element, el, is passed into the event handler function.

isReactive(object)

Check if an object is a reactive proxy.

watch(fn, [effectFn])

Run fn() once, and whenever fn's dependencies (see below) change, automatically rerun fn(), or, if effectFn provided, run effectFn(fn()).

fawc2ropas

Map<FunctionAssociatedWithContext, WeakMap<ReactiveObject, Set<PropertyAccess>>>. For each function-associated-with-context (FAWC), fawc2ropas stores all the reactive-object-property-accesses (ROPAs) within the function call. When any ROPA changes, the corresponding function of the FAWC reruns, and updates the correct position of the DOM with the help of its contextual info. fns of watchs also go into fawc2ropas.

Keep in mind that your FAWCs' returned value must rely only on ROPAs (like ro.p or ro[p]) within the FAWC, not on any other things like non-reactive object, free variable bindings (like let x = 1 inside the function), or global/closure variables.

You may never need to use fawc2ropas directly. It's for internal use, and is exposed only for debugging purposes.

ropa2fawcs

WeakMap<ReactiveObject, Record<PropertyAccess, WeakSet<FunctionAssociatedWithContext>>>. For each ROPA, ropa2fawcs stores all FAWCs it would trigger to rerun.

ropa2fawcs is purely for debugging purposes. It's not even actually used in hyper-arrow's own source code.