Solve: Explicit Resource Management and Safer Wasm Memory in Serverless JavaScript

Solve: Explicit Resource Management and Safer Wasm Memory in Serverless JavaScript

A New Chapter in Wasm Memory Safety

WebAssembly offers serious performance benefits inside serverless environments like Cloudflare Workers—but it also opens the door to memory management pitfalls. Developers used to JavaScript's automatic garbage collection must adapt to manual allocation and deallocation patterns that WebAssembly modules demand. And while FinalizationRegistry gave us a partial safety net, it was never meant to be a full seatbelt.

Now, JavaScript's upcoming Explicit Resource Management (ERM) proposal introduces a powerful, predictable, and expressive solution. With using blocks and standardized disposal protocols, ERM brings JavaScript closer to the structured cleanup paradigms long used in languages like C#, Python, and Rust. This article explores how ERM transforms Wasm memory safety—and how you can start preparing for it today.

The Problem with Finalization Alone

In Part 1, we showed how developers can use FinalizationRegistry in Workers to attach cleanup logic to Wasm-allocated memory: 

javascript

const cleanup = new FinalizationRegistry(({ptr, len}) => {
  free_buffer(ptr, len);
});

const buf = new Uint8Array(memory.buffer, ptr, len);
cleanup.register(buf, {ptr, len});

But as we noted, finalizers are non-deterministic. The JavaScript engine is under no obligation to invoke them promptly, or at all. That makes relying on FinalizationRegistry a gamble for anything critical. Even with Cloudflare’s execution safeguards (e.g. post-microtask scheduling and restricted finalizer behavior), you're still flying blind on timing.

Developers want a clear contract: allocate here, use here, clean up here. That's exactly what ERM provides.

Introducing ERM: How It Works

The ERM proposal standardizes a new protocol for releasing resources. It introduces a new keyword, using, and a well-defined disposal mechanism. Classes can implement Symbol.dispose or Symbol.asyncDispose to define what happens when the object goes out of scope.

Here's a simple, synchronous example: 

javascript

class WasmBuffer {
  constructor(ptr, len) {
    this.ptr = ptr;
    this.len = len;
  }

  [Symbol.dispose]() {
    free_buffer(this.ptr, this.len);
  }
}

{
  using buf = new WasmBuffer(ptr, len);
  // safely use buf within this block
} // automatic call to buf[Symbol.dispose]() here

Unlike FinalizationRegistry, this call is guaranteed. It runs deterministically at block exit, even if an exception is thrown inside the block. You can finally treat Wasm buffers like file handles or sockets: something you explicitly open and close.

For async resources like network handles or streaming writers, ERM also supports Symbol.asyncDispose, letting you use await using for deterministic async cleanup.

Why This Changes the Game for Workers and Wasm

When working in constrained environments like Cloudflare Workers, predictability is king. The event loop, memory caps, CPU time budgets—they all conspire to punish sloppiness. With ERM, you gain a model where cleanup happens when you say it does, not whenever the garbage collector gets around to it.

This is particularly important for WebAssembly, where memory leaks aren’t always obvious. Linear memory just grows and stays resident until you release it. The traditional advice to "wrap buffers in objects and use FinalizationRegistry as a backup" now becomes: wrap buffers in disposable classes and `` blocks for total control.

For example, combining ERM with a Wasm loader function: 

javascript

function createBuffer() {
  const ptr = make_buffer(lenPtr);
  const len = new DataView(memory.buffer).getUint32(lenPtr, true);
  return new WasmBuffer(ptr, len);
}

{
  using buf = createBuffer();
  const text = new TextDecoder().decode(new Uint8Array(memory.buffer, buf.ptr, buf.len));
  console.log(text);
} // memory is freed deterministically here

No leaks, no surprises.

What If ERM Isn’t Available Yet?

As of mid-2025, most JavaScript runtimes don't yet ship using and Symbol.dispose support. But we can prepare by adopting the shape of ERM patterns today. Here’s how to simulate the behavior using try/finally: 

javascript

class WasmBuffer {
  constructor(ptr, len) {
    this.ptr = ptr;
    this.len = len;
  }
  dispose() {
    free_buffer(this.ptr, this.len);
  }
}

const buf = new WasmBuffer(ptr, len);
try {
  const view = new Uint8Array(memory.buffer, buf.ptr, buf.len);
  console.log(new TextDecoder().decode(view));
} finally {
  buf.dispose(); // same guarantee, just more verbose
}

This scaffolding can later be upgraded to native using blocks with almost no logic changes—making it a smart transitional strategy.

Improving Development Workflow with Debug-Friendly Patterns

To deepen confidence in these patterns, developers can introduce lightweight visibility tools into their development workflow: 

javascript

class WasmBuffer {
  constructor(ptr, len) {
    this.ptr = ptr;
    this.len = len;
    console.log("Allocated WasmBuffer", ptr, len);
  }
  [Symbol.dispose]() {
    console.log("Disposing WasmBuffer", this.ptr, this.len);
    free_buffer(this.ptr, this.len);
  }
}

For local testing or wrangler dev sessions, this provides confirmation that disposal is happening as expected. Developers might count active buffers, tally successful disposals, or temporarily simulate disposal with mock behavior. These patterns improve debugging confidence without requiring formal memory profilers.

In a future post, we might package this into a helper tool or include a debugDispose() dev hook for rapid iteration.

Final Word

Explicit Resource Management isn’t just a syntactic convenience—it’s a philosophical upgrade. It brings JavaScript into alignment with the memory hygiene disciplines of Rust, Go, and modern C++. For those building on Workers with WebAssembly, ERM closes the loop on predictable resource lifecycles.

While not widely available yet, now is the time to embrace its patterns and prepare your code. By starting with the mindset of structured cleanup, you'll write code that's safer, easier to debug, and more predictable in performance under real-world serverless constraints.

Let FinalizationRegistry fade into the background. The future belongs to explicit, observable, and verifiable memory discipline.

And it starts with using.

Need Development Expertise?

We'd love to help you with your development projects.  Feel free to reach out to us at info@pacificw.com.

Written by Aaron Rose, software engineer and technology writer at Tech-Reader.blog.