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.