method

The method attribute allows you to describe methods of imported JavaScript objects. It is applied on a function that has this as its first parameter, which is a shared reference to an imported JavaScript type.

#[wasm_bindgen]
extern "C" {
    type Set;

    #[wasm_bindgen(method)]
    fn has(this: &Set, element: &JsValue) -> bool;
}

This generates a has method on Set in Rust, which invokes the Set.prototype.has method in JavaScript.

let set: Set = ...;
let elem: JsValue = ...;
if set.has(&elem) {
    ...
}