JavaScript's New Superpower: Explicit Resource Management

Their first example is about having to have a try/finally block in a function like this:

    function processData(response) {
        const reader = response.body.getReader();
        try {
            reader.read()
        } finally {
            reader.releaseLock();
        }
    }

So that the read lock is lifted even if reader.read() throws an error.

Does this only hold for long running processes? In a browser environment or in a cli script that terminates when an error is thrown, would the lock be lifted when the process exits?

This seems error-prone, for at least two reasons:

* If you accidentally use `let` or `const` instead of `using`, everything will work but silently leak resources.

* Objects that contain resources need to manually define `dispose` and call it on their children. Forgetting to do so will lead to resource leaks.

It looks like defer dressed up to resemble RAII.

Can someone explain why they didn’t go with (anonymous) class destructors? Or something other than a Symbol as special object key. Especially when there are two Symbols (different one for asynchronous) which makes it a leaky abstraction, no?

Still implemented with the super villain language, c++?

This is a great upcoming feature, I wrote some practical advice (a realistic example, how to use it with TypeScript/vite/eslint/neovim/etc…) about it a few months ago here: https://abstract.properties/explicit-resource-management-is-...

Need to dig into this more, but I built OneJS [1] (kinda like React Native but for Unity), and at first glance this looks perfect for us(?). Seems to be super handy for Unity where you've got meshes, RenderTextures, ComputeBuffers, and NativeContainers allocations that all need proper disposal outside of JS. Forcing disposal at lexical scopes, we can probs keep memory more stable during long Editor sessions or when hot-reloading a lot.

[1] https://github.com/Singtaa/OneJS

Remind me of C#.. IDisposible and IAsyncDisposible in C# helps a lot to write good mechanisms for things that should actually be abstracted in a nice way (such as locks handling, queue mechanisms, temporary scopes for impersonation, etc).

Context managers: exist.

JS: drop but we couldn't occupy a possibly taken name, Symbol for the win!

It's hilariously awkward.

JavaScript new features: segmentation faults, memory leaks, memory corruption and core dumps.

Maybe it's just me, but [Symbol.dispose]() seems like a really hacky way to add that functionality to an Object. Here's their example:

    using readerResource = {
        reader: response.body.getReader(),
        [Symbol.dispose]() {
            this.reader.releaseLock();
        },
    };

First, I had to refresh my memory on the new object definition shorthand: In short, you can use a variable or expression to define a key name by using brackets, like: let key = "foo"; { [key]: "bar"}, and secondly you don't have to write { "baz" : function(p) { ... } }, you can instead write { baz(p) {...} }. OK, got it.

So, if I'm looking at the above example correctly, they're implementing what is essentially an Interface-based definition of a new "resource" object. (If it walks like a duck, and quacks...)

To make a "resource", you'll tack on a new magical method to your POJO, identified not with a standard name (like Object.constructor() or Object.__proto__), but with a name that is a result of whatever "Symbol.dispose" evaluates to. Thus the above definition of { [Symbol.dispose]() {...} }, which apparently the "using" keyword will call when the object goes out of scope.

Do I understand that all correctly?

I'd think the proper JavaScript way to do this would be to either make a new object specific modifier keyword like the way getters and setters work, or to create a new global object named "Resource" which has the needed method prototypes that can be overwritten.

Using Symbol is just weird. Disposing a resource has nothing to do with Symbol's core purpose of creating unique identifiers. Plus it looks fugly and is definitely confusing.

Is there another example of an arbitrary method name being called by a keyword? It's not a function parameter like async/await uses to return a Promise, it's just a random method tacked on to an Object using a Symbol to define the name of it. Weird!

Maybe I'm missing something.

So… drop

I would like to petition JSLand to please let go of the word "use" and all of its derivatives. Cool feature though, looking forward to using (smh) it.