signal-utils/src/weak-map.ts

Utils for use with the Signals Proposal: https://github.com/proposal-signals/proposal-signals

import { createStorage, type StorageWeakMap } from "./-private/util.ts";

export class SignalWeakMap<K extends object = object, V = unknown>
  implements WeakMap<K, V>
{
  private storages: StorageWeakMap<K> = new WeakMap();

  private vals: WeakMap<K, V>;

  private readStorageFor(key: K): void {
    const { storages } = this;
    let storage = storages.get(key);

    if (storage === undefined) {
      storage = createStorage();
      storages.set(key, storage);
    }

    storage.get();
  }

  private dirtyStorageFor(key: K): void {
    const storage = this.storages.get(key);

    if (storage) {
      storage.set(null);
    }
  }

  constructor();
  constructor(iterable: Iterable<readonly [K, V]>);
  constructor(entries: readonly [K, V][] | null);
  constructor(
    existing?: readonly [K, V][] | Iterable<readonly [K, V]> | null | undefined,
  ) {
    // TypeScript doesn't correctly resolve the overloads for calling the `Map`
    // constructor for the no-value constructor. This resolves that.
    this.vals = existing ? new WeakMap(existing) : new WeakMap();
  }

  get(key: K): V | undefined {
    this.readStorageFor(key);

    return this.vals.get(key);
  }

  has(key: K): boolean {
    this.readStorageFor(key);

    return this.vals.has(key);
  }

  set(key: K, value: V): this {
    this.dirtyStorageFor(key);

    this.vals.set(key, value);

    return this;
  }

  delete(key: K): boolean {
    this.dirtyStorageFor(key);

    return this.vals.delete(key);
  }

  get [Symbol.toStringTag](): string {
    return this.vals[Symbol.toStringTag];
  }
}

// So instanceof works
Object.setPrototypeOf(SignalWeakMap.prototype, WeakMap.prototype);