Hot reloading disposal events

hotness.ts

/*
MIT No Attribution

Copyright 2024 Thomas Aylott

Permission is hereby granted, free of charge, to any person obtaining a copy of this
software and associated documentation files (the "Software"), to deal in the Software
without restriction, including without limitation the rights to use, copy, modify,
merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/

type RefObject<T> = { readonly current: T }
declare global {
  var hotness: undefined | RefObject<Hotness>
}

type HotDisposable<T> = T & {
  [Symbol.dispose](this: T, last: T, next: T): void
}

export class Hotness {
  static version = "hotness 2.13"
  version = Hotness.version

  count = -1

  disposables = new Map<string, HotDisposable<any>>()
  listeners: (null | (() => void))[] = [];

  [Symbol.dispose]() {
    this.listeners.forEach((it, i, them) => ((them[i] = null), it?.()))
    this.listeners = []
  }

  using<T extends Record<string, HotDisposable<any>>>(meta: ImportMeta, map: T): T {
    for (const [id, current] of Object.entries(map)) this.usingOne(meta, id, current)
    return map
  }

  usingOne<T extends HotDisposable<any>>({ filename }: ImportMeta, id: string, current: T): T {
    const key = `${filename}#${id}`
    const old = this.disposables.get(key)
    this.disposables.set(key, current)
    try {
      old?.[Symbol.dispose]?.(old, current)
    } catch (error) {
      console.warn("Hotness.using", "error disposing", { key, error })
    }
    return current
  }

  static get current(): Hotness {
    const old = globalThis.hotness?.current
    if (old?.version === Hotness.version) return old

    globalThis.hotness = { current: new Hotness() }
    return globalThis.hotness!.current
  }

  static onHotReload(listener: (old: Hotness, current: Hotness) => void): void {
    const old = { ...Hotness.current } as Hotness
    Hotness.current.listeners.push(() => listener(old, Hotness.current))
  }
}

Hotness.current.count++
Hotness.current[Symbol.dispose]()

if (import.meta.main) {
  console.log(`<TEST id=${Hotness.current.count}>`, import.meta.filename)
  setImmediate(() => Hotness.onHotReload(({ count }) => console.log(`</TEST id=${count}>\n`)))

  const testObject: HotDisposable<{ id: string }> = {
    id: new Date().toLocaleTimeString() + " " + Hotness.current.count,
    [Symbol.dispose]: function ({ id: OLD }, { id: NEW }): void {
      console.log("Hot reloaded! disposed of old object.", { OLD, NEW })
    },
  }

  Hotness.current.using(import.meta, { testObject })

  Hotness.onHotReload(({ count, version }) => {
    console.log("onHotReload, Hot reloaded! ran once listener. ", { count, version })
  })
}