The constructor attribute is used to indicate that the function being bound should actually translate to calling the new operator in JavaScript. The final argument must be a type that's imported from JavaScript, and it's what will get used in the generated glue:

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

    #[wasm_bindgen(constructor)]
    fn new() -> Shoes;
}
}

This will attach a new static method to the Shoes type, and in JavaScript when this method is called, it will be equivalent to new Shoes().

#![allow(unused_variables)]
fn main() {
// Become a cobbler; construct `new Shoes()`
let shoes = Shoes::new();
}