How to access data descriptor properties of a JS class instance?

[Jules-Bertholet]

Summary

With wasm-bindgen it is easy to get properties of classes accessed by getters. For example,

#[wasm_bindgen]
extern "C" {
    pub type Foo;

    #[wasm_bindgen(method, getter)]
    fn bar(this: &Foo) -> String;
}

allows using the getter for property bar of Foo from Rust.

But what if the object property is a simple data descriptor, as opposed to having getter or setter methods? How can one access the property from Rust then (other than with Reflect)? I've searched the docs but haven't found anything.

[alexcrichton]

I believe both this syntax and Reflect will work, both translate to a field access of foo.bar in JS

[Jules-Bertholet]

@alexcrichton The first syntax only works (at least in my testing) if my_foo.bar is a property assessed with getters and setters, because the generated JS uses getOwnPropertyDescriptor to retrieve the getter/setter. But if bar doesn't have getters and setters, and is just a normal data descriptor (with value and a writable), this doesn't work. And Reflect is unwieldy, and loses type information.

[alexcrichton]

You may need to add structural to the attribute, but I thought that was the default nowadays...

[Jules-Bertholet]

You may need to add structural to the attribute, but I thought that was the default nowadays...

Ah, thanks! I had added final—the object I was using was frozen, so I thought final would suit my usage... Maybe the documentation in this area should be improved?

[alexcrichton]

Seems reasonable to me!