current.rs

  use wasm_bindgen::prelude::Closure;
  use wasm_bindgen::JsCast;
  use web_sys::{Document, EventTarget};

  let document = Document::new().map_err(|_| ErrorKind::Document)?;
  let target: EventTarget = document.into();

  let cb = Closure::wrap(Box::new(move || {
    println!("hello world from WASM");
  }) as Box<Fn()>);

  let event_name = "DOMContentLoaded";
  target
    .add_event_listener_with_callback(event_name, cb.as_ref().unchecked_ref())
    .map_err(|_| ErrorKind::Document)?;

expected.rs

use dom::{self, Document, Events};

let document = Document::new()?;
let event = Events::DomContentLoaded;
document.add_event_listener(event, |_| {
  println!("DOM Loaded!");
})?;