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state.js
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state.js
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const abortRegistry = new FinalizationRegistry(controller => controller.abort())
const camelToKebab = string => string.replace(/([a-z])([A-Z])/g, (_, a, b) => `${a}-${b.toLowerCase()}`)
const kebabToCamel = string => string.replace(/([a-z])-([a-z])/g, (_, a, b) => a+b.toUpperCase())
export class ChangeEvent extends Event {
#final
constructor(...changes) {
super('change')
this.changes = changes
}
get final() {
if (!this.#final) {
this.#final = new Map(this.changes)
}
return this.#final
}
}
export class SimpleState extends EventTarget {}
export class MapStorage extends Storage {
#map = new Map()
key(index) {
return [...this.#map.keys()][index]
}
getItem(keyName) {
if (this.#map.has(keyName))
return this.#map.get(keyName)
else
return null
}
setItem(keyName, keyValue) {
this.#map.set(keyName, String(keyValue))
}
removeItem(keyName) {
this.#map.delete(keyName)
}
clear() {
this.#map.clear()
}
}
export class State extends SimpleState {
#target
#options
#queue
#forwardCache
#abortController
#nested = new Map()
#weakRef = new WeakRef(this)
static isState(object) { return SimpleState.prototype.isPrototypeOf(object) }
constructor(target={}, options={}) {
super()
this.#abortController = new AbortController
abortRegistry.register(this, this.#abortController)
this.#options = options
this.#target = target
this.values = new Proxy(target, {
set: (_target, prop, value) => {
const old = this.get(prop)
if (old !== value) {
this.emit(prop, value)
if (this.#options.shallow) {
if (State.isState(old)) this.disown(prop, old)
if (State.isState(value)) this.adopt(prop, value)
}
this.set(prop, value)
}
return true
},
get: (_target, prop) => this.get(prop),
})
this.addEventListener
// Try running a "<name>Changed" method for every changed property
// Can be disabled to maybe squeeze out some performance
if (options.methods ?? true) {
this.addEventListener("change", ({final}) => {
final.forEach((value, prop) => {
if (`${prop}Changed` in this) this[`${prop}Changed`](value)
})
})
}
}
// When you only need one value, you can skip the proxy.
set value(value) { this.values.value = value }
get value() { return this.values.value }
adopt(prop, state) {
let handlers = this.#nested.get(state)
if (!handlers) {
// Actual adoption
handlers = new Map()
this.#nested.set(state, handlers)
}
const ref = this.#weakRef
const handler = () => ref.deref()?.emit(prop, state)
handlers.set(prop, handler)
state.addEventListener("change", handler, {signal: this.#abortController.signal})
}
disown(prop, state) {
const handlers = this.#nested.get(state)
const handler = handlers.get(prop)
state.removeEventListener("change", handler)
handlers.delete(prop)
if (handlers.size == 0) {
this.#nested.delete(state)
}
}
// Anounces that a prop has changed
emit(prop, value) {
if (this.#options.defer ?? true) {
if (!this.#queue) {
this.#queue = []
queueMicrotask(() => {
this.dispatchEvent(new ChangeEvent(...this.#queue))
this.#queue = undefined
})
}
this.#queue.push([prop, value])
} else {
this.dispatchEvent(new ChangeEvent([prop, value]))
}
}
forward(property="value", fallback) {
if (!this.#forwardCache) this.#forwardCache = new Map()
const cached = this.#forwardCache.get(property)?.deref()
if (cached) {
return cached
} else {
const forwarded = new ForwardState(this, property, fallback)
const ref = new WeakRef(forwarded)
this.#forwardCache.set(property, ref)
forwardFinalizationRegistry.register(forwarded, [this.#forwardCache, property])
return forwarded
}
}
set(...args) {
if (args.length === 1) return this.set("value", ...args)
const [prop, value] = args
this.#target[prop] = value
}
get(...args) {
if (args.length === 0) return this.get("value")
const prop = args[0]
return this.#target[prop]
}
subscribe(prop, callback) {
if (!callback) return this.subscribe("value", prop)
const controller = new AbortController()
this.addEventListener("change", ({final}) => {
if (final.has(prop)) return callback(final.get(prop))
}, {signal: controller.signal})
callback(this.value)
return () => controller.abort()
}
// Backwards compatibility
get proxy() { return this.values }
}
const forwardFinalizationRegistry = new FinalizationRegistry(([cache, name]) => {
cache.remove(name)
})
export class ForwardState extends SimpleState {
#backend
#property
#fallback
constructor(backend, property, fallback) {
super()
this.#backend = backend
this.#property = property
this.#fallback = fallback
const ref = new WeakRef(this)
const abortController = new AbortController()
backend.addEventListener("change", event => {
const state = ref.deref()
if (state) {
const relevantChanges = event.changes
.filter(([name]) => name === property)
.map(([_, value]) => ["value", value])
if (relevantChanges.length > 0)
state.dispatchEvent(new ChangeEvent(...relevantChanges))
} else {
abortController.abort()
}
}, {signal: abortController.signal})
}
get value() { return this.#backend.values[this.#property] ?? this.#fallback }
set value(value) { this.#backend.values[this.#property] = value }
}
class StorageChangeEvent extends Event {
constructor(storage, key, value, targetState) {
super("storagechange")
this.storageArea = storage
this.key = key
this.newValue = value
this.targetState = targetState
}
}
export class StoredState extends State {
#storage
constructor(init, options={}) {
super({}, options)
this.#storage = options.storage ?? localStorage ?? new MapStorage()
// Initialise storage from defaults
for (const [prop, value] of Object.entries(init)) {
if (this.#storage[prop] === undefined)
this.set(prop, value)
}
// Emit change events for any changed keys
for (let i=0; i<this.#storage.length; i++) {
const key = this.#storage.key(i)
const value = this.#storage[key]
if (value !== JSON.stringify(init[key]))
this.emit(key, value)
}
// Listen for changes from other windows
const handler = event => {
if (event.targetState !== this && event.storageArea == this.#storage) {
this.emit(event.key, JSON.parse(event.newValue))
}
}
addEventListener("storage", handler)
addEventListener("storagechange", handler)
}
set(prop, value) {
const json = JSON.stringify(value)
dispatchEvent(new StorageChangeEvent(this.#storage, prop, json, this))
this.#storage[prop] = json
}
get(prop) {
const value = this.#storage[prop]
return value && JSON.parse(value)
}
}
const attributeObserver = new MutationObserver(mutations => {
for (const {type, target, attributeName: name} of mutations) {
if (type == "attributes") {
const next = target.getAttribute(name)
const camelName = kebabToCamel(name)
if (String(target.state.values[camelName]) !== next)
target.state.values[camelName] = next
}
}
})
export const component = (generator, name) => {
name = name ?? camelToKebab(generator.name)
const Element = class extends HTMLElement{
constructor() {
super()
this.state = new State(Object.fromEntries([...this.attributes].map(attribute => [kebabToCamel(attribute.name), attribute.value])))
this.state.addEventListener("change", event => {
for (const [name, value] of event.changes) {
const kebabName = camelToKebab(name)
if (this.getAttribute(kebabName) !== String(value))
this.setAttribute(kebabName, value)
}
})
attributeObserver.observe(this, {attributes: true})
this.replaceChildren(generator(this))
}
}
customElements.define(name, Element)
return Element;
}
class ComposedState extends SimpleState {
#func
#states
#options
constructor(func, options, ...states) {
super()
this.#func = func
this.#states = states
this.#options = options
const abortController = new AbortController()
abortRegistry.register(this, abortController)
const ref = new WeakRef(this)
states.forEach(state => {
state.addEventListener("change", event => {
const value = event.final.get("value")
if (value) ref.deref()?.scheduleUpdate()
}, {signal: abortController.signal})
})
this.update()
}
#microtaskQueued
scheduleUpdate() {
if (this.#options.defer) {
if (!this.#microtaskQueued) {
queueMicrotask(() => {
this.#microtaskQueued = false
this.update()
})
}
this.#microtaskQueued = true
} else {
this.update()
}
}
update() {
this.value = this.#func(...this.#states.map(state => state.value))
this.dispatchEvent(new ChangeEvent([["value", this.value]]))
}
}
export const compose = func => (...states) => new ComposedState(func, {defer: true}, ...states)
const eventName = "mutation"
class MutationEvent extends Event {
constructor() {
super(eventName, {bubbles: true})
}
}
const mutationObserver = new MutationObserver(mutations => {
for (const mutation of mutations) {
mutation.target.dispatchEvent(new MutationEvent())
}
})
export class DOMState extends SimpleState {
#target
#defer
#getValue
#equal
#old
#changedValue = false
constructor(target, options) {
super()
this.#defer = options.defer ?? false
this.#target = target
this.#getValue = options.get ?? (target => target.value)
this.#equal = options.equal ?? ((a, b) => a===b)
this.#old = this.#getValue(target)
const controller = new AbortController()
target.addEventListener(eventName, event=>{this.update(event)}, {signal: controller.signal})
abortRegistry.register(this, controller)
mutationObserver.observe(target, {
attributes: true,
childList: true,
characterData: true,
subtree: true,
})
}
get value() { return this.#old }
update() {
const current = this.#getValue(this.#target)
if (this.#equal(this.#old, current)) return
this.#old = current
if (this.#defer) {
if (!this.#changedValue) {
queueMicrotask(() => {
this.#changedValue = false
this.dispatchEvent(new ChangeEvent(["value", this.#changedValue]))
})
this.#changedValue = current
}
} else {
this.dispatchEvent(new ChangeEvent(["value", current]))
}
}
}
export default State