shiva

shiva

shiva is a minimal JavaScript library (2.5KB gzipped) for building reactive user interfaces - no template language, no virtual DOM. It is built on a simple premise: the DOM API is already a capable interface, what would a thin wrapper with a more ergonomic syntax look like?

So instead of:

<div>Hi there 👋</div>

shiva provides a function called div():

import { div } from "shiva"

const element = div("Hi there 👋")

Nested

import { div } from "shiva"

const nestedHTMLDivElement = div(
    div("Hi there 👋"),
    div("Hi there 👋"),
)

This will produce:

<div>
    <div>Hi there 👋</div>
    <div>Hi there 👋</div>
</div>

shiva will append HTML elements if they are passed as an argument. It will create and append a textNode element if a string is passed.

Mixed content

Strings and elements can be mixed freely as arguments. Order is preserved:

import { p, strong } from "shiva"

const sentence = p("The value is ", strong("42"), " and that's final.")

This produces:

<p>The value is <strong>42</strong> and that's final.</p>

Attributes

To pass attributes to an element:

import { div } from "shiva"

const handler = () => {
    console.log("handled it 👊")
}

const superDiv = div("Hi there 👋", { 
    onclick: handler,
    className: "mr-2",
    id: "Super Div 🦸‍♂️",
    style: {
        fontSize: "3rem"
    }
})

shiva will apply attributes if an object is passed as one of the arguments.

Elements

shiva provides:

• div()
• img()
• p()
• h1()
• h2()
• h3()
• h4()
• h5()
• h6()
• b()
• strong()
• i()
• em()
• a()
• ul()
• ol()
• li()
• span()
• br()
• code()
• pre()
• button()

To create other HTML elements not included in the API, shiva provides a more generic element() function.

import { element } from "shiva"

const section = element("section", "I am a section")

Any HTML element, including custom elements, can be created.

Components

Any function that returns a HTML element is a component:

import { div, h2, p } from "shiva"

const card = (title, body) => div(h2(title), p(body))

const page = div(
    card("Hello", "First card"),
    card("World", "Second card"),
)

Components are plain functions — no lifecycle, no decorators, no special syntax. Each component just needs to return an HTMLElement (or array of elements) to be composed into a parent.

Installation

npm install shiva

shiva is distributed as an ES module. Please use a module aware build tool to import.

See ./consumer for an example of how to include shiva in a project.

Getting started

Create root element

To append a root element to document.body, pass { root: true } as an option:

import { div } from "shiva"

const app = () => {
    div({ root: true },
        componentA(),
        componentB()
    )
}

app()

This appends a <div> to the page body with componentA and componentB nested inside.

👉 componentA and componentB must return a HTML element or array of HTML elements to be appended to the parent.

Reactive state with signals

shiva provides a signal factory for reactive state. A signal holds a value and notifies subscribers automatically when it changes.

import { signal, p, code } from "shiva"

const count = signal(0)

const counter = p(code(count))
// counter.textContent updates automatically when count changes

count.set(1) // counter now shows "1"

subscribe returns an unsubscribe function to stop listening:

const unsubscribe = count.subscribe(() => {
    console.log(count.get())
})

unsubscribe() // stops the listener

Object signals with reactive fields

When signal is given an object, every field becomes its own reactive signal. Pass field signals directly to elements - they update independently when only their value changes.

import { signal, h2, p } from "shiva"

const data = signal({ heading: "Hello", body: "World" })

const { heading, body } = data

const view = p(h2(heading), body)

data.set({ heading: "Updated", body: "World" })
// only the h2 updates - body is unchanged and does not re-render

Field signals can also be set individually, writing back to the parent signal:

heading.set("Just the heading")
// data.get().heading === "Just the heading"
// body is unaffected

Deeply nested reactive fields

Object signals are recursive. Nested objects also become reactive - field access chains as deep as the data structure:

import { signal, p } from "shiva"

const data = signal({
    meta: {
        title: "shiva",
        description: "A minimal UI library"
    }
})

const { meta } = data
const { title, description } = meta

const view = p(title, " - ", description)

data.set({
    meta: {
        title: "shiva",
        description: "No virtual DOM"
    }
})
// only description updates - title did not change

Writing back through a nested field signal propagates to the root:

description.set("Updated")
// data.get().meta.description === "Updated"

Reactive style

A signal can be passed as a style value to reactively update an element's styles.

import { signal, div } from "shiva"

const style = signal({ color: "crimson", fontSize: "2rem" })

const el = div("hello", { style })

style.set({ color: "royalblue", fontSize: "2rem" }) // el style updates in place

Individual style properties can also be signals:

const color = signal("crimson")

const el = div("hello", { style: { color } })

color.set("royalblue") // only color updates

Reactive attributes

The same patterns apply to attributes:

import { signal, div } from "shiva"

const attributes = signal({ "data-count": "0", id: "counter" })

const el = div("hello", { attributes })

attributes.set({ "data-count": "1", id: "counter" }) // attributes update in place

Individual attribute values can also be signals:

const dataCount = signal("0")

const el = div("hello", { attributes: { "data-count": dataCount } })

dataCount.set("1") // only data-count updates

Signal API

// Primitive signal
const s = signal(0)

s.get(): T
s.set(value: T): void
s.subscribe(fn: () => void): () => void  // returns unsubscribe

// Object signal - every field is also a signal
const s = signal({ name: "Alice", age: 30 }): ReactiveSignal<{ name: string, age: number }>

s.name.get()           // "Alice"
s.name.set("Bob")      // updates name, notifies name subscribers
s.name.subscribe(fn)   // subscribe to name changes only
s.get()                // { name: "Alice", age: 30 }
s.set({ name: "Bob", age: 30 }) // replace whole object

Note: The field names get, set, and subscribe are reserved and cannot be used as keys in objects passed to signal().

isSignal

A type guard for duck-typed signal detection:

import { signal, isSignal } from "shiva"

isSignal(signal(0))  // true
isSignal({ get: () => 0, set: () => {}, subscribe: () => () => {} })  // true
isSignal("hello")    // false

State (pubsub)

shiva also provides a simple publish / subscribe utility.

pubsub() returns an array where the first element is the subscribe function and the second element is the publish function.

import { pubsub } from "shiva"

const [subscribe, publish] = pubsub([1, 2, 4, 5])

subscribe(data => {
    console.log(data)
    // logs the value passed to publish()
})

// some time later
publish([6,7,9,12]) // logs [6,7,9,12]

API

pubsub<T>(
    initial?: T,
    reducer?: (current: T, next: T) => T
): [(callback: (state: T) => void) => void, (payload: T) => T]

Initialise state with initial.

Run a function on new state with a reducer function. Can be used for more complex logic or when the next state depends on the previous one.

const reducer = (state, newState) => state + newState

const [subscribe, publish] = pubsub("DOGE", reducer)

subscribe(state => {
    console.log(state)
})

publish(" to the moon 🚀") // logs "DOGE to the moon 🚀" 

Global store

Extending the publish / subscribe pattern across components creates a global store, useful if you don't want to pass subscribers and publishers through nested components.

shiva provides a createStore() function to create this global store.

// global-store.js
import { createStore } from "shiva"

const globalStore = createStore("🌍")

export default globalStore

Now subscribe or publish to this store.

// another file
import globalStore from "./global-store"

const [subscriberGlobal, publishGlobal] = globalStore

Here we can name the subscribe / publish functions, note we don't call the globalStore, it is already a subscribe / publish tuple.

TypeScript

shiva ships with type definitions. Types are available for import:

import { signal } from "shiva"
import type { Signal, ReactiveSignal, ReactiveStyle, ContainerOptions } from "shiva"

const count: Signal<number> = signal(0)

const style = signal<ReactiveStyle>({ color: "blue" })

type User = { name: string; age: number }
const user: ReactiveSignal<User> = signal({ name: "Alice", age: 30 })
// user.name is Signal<string>, user.age is Signal<number>

Tree shaking

shiva is marked as side-effect free. Bundlers like webpack, rollup, and vite will tree-shake unused exports.

License

MIT license