purify.js

Simple, not Familiar

Experimental: Not for Production

purify.js is a 1.0kB (minified, gzipped) JavaScript UI building library that encourages the usage of pure JavaScript and DOM, while providing a thin layer of abstraction for the annoying parts for better DX (developer experience).

Compare

Size ⚡

Library	.min.js	.min.js.gz
purify.js	2.3kB	1.0kB
Preact 10.19.3	11.2kB	4.5kB
Solid 1.8.12	23kB	8.1kB
jQuery 3.7.1	85.1kB	29.7kB
Vue 3.4.15	110.4kB	40kB
ReactDOM 18.2.0	130.2kB	42kB
Angular 17.1.0	310kB	104kB

Syntax

Compare Syntax

Installation 🍙

To install purify.js, follow the jsr.io/@purifyjs/core.

Examples 🍤

Counter

import { computed, Lifecycle, ref, Signal, tags } from "@purifyjs/core"

const { div, section, button, ul, li, input } = tags

function App() {
    return div().id("app").children(Counter())
}

function Counter() {
    const count = ref(0)
    const double = count.derive((count) => count * 2)
    const half = computed(() => count.val * 0.5)

    return div().children(
        section({ class: "input" })
            .ariaLabel("Input")
            .children(
                button()
                    .title("Decrement by 1")
                    .onclick(() => count.val++)
                    .textContent("-"),
                input().type("number").effect(useBindNumber(count)).step("1"),
                button()
                    .title("Increment by 1")
                    .onclick(() => count.val++)
                    .textContent("+")
            ),
        section({ class: "output" })
            .ariaLabel("Output")
            .children(
                ul().children(
                    li().children("Count: ", count),
                    li().children("Double: ", double),
                    li().children("Half: ", half)
                )
            )
    )
}

function useBindNumber(
    state: Signal.State<number>
): Lifecycle.OnConnected<HTMLInputElement> {
    return (element) => {
        const listener = () => (state.val = element.valueAsNumber)
        element.addEventListener("input", listener)
        const unfollow = state.follow((value) => (element.valueAsNumber = value), true)
        return () => {
            element.removeEventListener("input", listener)
            unfollow()
        }
    }
}

document.body.append(App().element)

ShadowRoot

import { fragment, ref, tags } from "@purifyjs/core"

const { div, button } = tags

function App() {
    return div().id("app").children(Counter())
}

function Counter() {
    const host = div()
    const shadow = host.element.attachShadow({ mode: "open" })

    const count = ref(0)

    shadow.append(
        fragment(
            button()
                .title("Click me!")
                .onclick(() => count.val++)
                .children("Count:", count)
        )
    )
    return host
}

document.body.append(App().element)

Guide 🥡

Coming soon.

Why Not JSX Templating? 🍕

Lack of Type Safety: An <img> element created with JSX cannot have the HTMLImageElement type because all JSX elements must return the same type. This causes issues if you expect a HTMLImageElement some where in the code but all JSX returns is HTMLElement or something like JSX.Element. Also, it has some other issues related to the generics, discriminated unions and more.
Build Step Required: JSX necessitates a build step, adding complexity to the development workflow. In contrast, purify.js avoids this, enabling a simpler and more streamlined development process by working directly with native JavaScript and TypeScript.
Attributes vs. Properties: In purify.js, I can differentiate between attributes and properties of an element while building it, which is not currently possible with JSX. This distinction enhances clarity and control when defining element characteristics.

Current Limitations 🦀

Lifecycle and Reactivity: Currently, I use Custom Elements to detect if an element is connected to the DOM. This means:
- Every element created by the tags proxy, are Custom Elements. But they look like normal <div>(s) and <span>(s) and etc on the DevTools, because they extend the original element and use the original tag name. This way we can follow the life cycle of every element. And it works amazingly.
- But we also have signals, which might not return an HTMLElement. So we gotta wrap signals with something in the DOM. So we can follow its lifecycle and know where it starts and ends. Traditionally this is done via Comment Node(s). But there is no feasible and sync way to follow a Comment Node on the DOM while also allowing direct DOM manipulation (DOM#533). So instead of Comment Node(s), I used Custom Elements with display: contents style to wrap signal renders. This way, I can follow the lifecycle of the signal render in the DOM, and decide to follow or unfollow the signal. Since signal render itself is an Element this approach has limitations, such as .parent > * selector wouldn't select all children if some are inside a signal.
  
  As another solution to this, a persistent DocumentFrament that acts similar to Element with display: contents style but also intentionally skipped by query selectors would also be useful. Similar: (DOM#739)

But as long as the developer is aware of this limitation or difference, it shouldn't cause any issues.