The no_deref attribute can be used to say that no Deref impl should be generated for an imported type. If this attribute is not present, a Deref impl will be generated with a Target of the type's first extends attribute, or Target = JsValue if there are no extends attributes.

#![allow(unused_variables)]
fn main() {
#[wasm_bindgen]
extern "C" {
    type Foo;

    #[wasm_bindgen(method)]
    fn baz(this: &Foo)

    #[wasm_bindgen(extends = Foo, no_deref)]
    type Bar;
}

fn do_stuff(bar: &Bar) {
    bar.baz() // Does not compile
}

}