enso/detached/index.js

Maximalist state & form management library for React

export const detachedValue = Symbol();
export class UndefinedStateRegistry {
  #external;
  #refsMap = new Map();
  #registry = new FinalizationRegistry(key => this.#refsMap.delete(key));
  constructor(external) {
    this.#external = external;
  }
  register(key, atom) {
    const ref = new WeakRef(atom);
    this.#refsMap.set(key, ref);
    this.#registry.register(ref, key);
  }
  claim(key) {
    // Look up if the undefined atom exists
    const ref = this.#refsMap.get(key);
    const registered = ref?.deref();
    if (!ref || !registered) return;

    // Unregister the atom and allow the caller to claim it
    this.#registry.unregister(ref);
    this.#refsMap.delete(key);
    return registered;
  }
  ensure(key) {
    // Try to look up registered undefined item
    const registered = this.#refsMap.get(key)?.deref();
    if (registered) return registered;

    // Or create and register a new one
    const atom = this.#external.constructor.create(detachedValue, {
      key,
      [this.#external.constructor.prop]: this.#external
    });
    this.register(key, atom);
    return atom;
  }
}