The js_class attribute is used to indicate that all the methods inside an impl block should be attached to the specified JS class instead of inferring it from the self type in the impl block. The js_class attribute is most frequently paired with the js_name attribute on structs:

# #![allow(unused_variables)]
#fn main() {
#[wasm_bindgen(js_name = Foo)]
pub struct JsFoo { /* ... */ }

#[wasm_bindgen(js_class = Foo)]
impl JsFoo {
    #[wasm_bindgen(constructor)]
    pub fn new() -> JsFoo { /* ... */ }

    pub fn foo(&self) { /* ... */ }
}
#}

which is accessed like:

# #![allow(unused_variables)]
#fn main() {
import { Foo } from './my_module';

const x = new Foo();
x.foo();
#}