SafeHandle

1. SafeHandle-simple-public.js

// a simple SafeHandle with a public `dangerousGetHandle` method.
class SafeHandle {
  static #finalizer = new FinalizationRegistry(({ handle, releaseHandle }) => {
    releaseHandle(handle);
  });

  #data = null;

  constructor(handle, releaseHandle) {
    this.#data = { handle, releaseHandle };
    SafeHandle.#finalizer.register(this, this.#data, this);
  }

  get disposed() {
    return this.#data === null;
  }

  // public, so anyone could get the handle
  dangerousGetHandle() {
    if (this.#data === null) throw new ReferenceError("Object is disposed");
    return this.#data.handle;
  }

  dispose() {
    if (this.#data !== null) {
      SafeHandle.#finalizer.unregister(this);
      const { handle, releaseHandle } = this.#data;
      this.#data = null;
      releaseHandle(handle);
    }
  }

  [Symbol.dispose]() {
    return this.dispose();
  }
}

// usage:
function cleanupHandle(unsafeHandle) { ... }

class MyHandle extends SafeHandle {
  constructor(handle) {
    super(handle, cleanupHandle);
  }
  
  read() {
    // dangerousGetHandle guards against disposal for you
    return nativeMethods.read(this.dangerousGetHandle());
  }
}

2. SafeHandle-simple-private.js

// a simple SafeHandle without a public method to access the handle.
class SafeHandle {
  static #finalizer = new FinalizationRegistry(({ handle, releaseHandle }) => {
    releaseHandle(handle);
  });

  #data = null;

  constructor(handle, releaseHandle) {
    this.#data = { handle, releaseHandle };
    SafeHandle.#finalizer.register(this, this.#data, this);
  }

  get disposed() {
    return this.#data === null;
  }

  dispose() {
    if (this.#data !== null) {
      SafeHandle.#finalizer.unregister(this);
      const { handle, releaseHandle } = this.#data;
      this.#data = null;
      releaseHandle(handle);
    }
  }

  [Symbol.dispose]() {
    return this.dispose();
  }
}

// usage:
function cleanupHandle(unsafeHandle) { ... }

class MyHandle extends SafeHandle {
  #handle;
  constructor(handle) {
    super(handle, cleanupHandle);
    this.#handle = handle;
  }

  // no public superclass method, so we use our own private method
  // to guard against disposal
  #dangerousGetHandle() {
    if (super.disposed) throw new ReferenceError("Object disposed.");
    return this.#handle;
  }
  
  read() {
    return nativeMethods.read(this.#dangerousGetHandle());
  }
}