bevyengine/bevy · error

Should register `setTimeout`.

Error message

Should register `setTimeout`.

What it means

An expect() failure inside the wasm32 schedule runner build path: the code reaches a branch that requires a registered setTimeout callback (via web_sys::window()), but the browser window/global is unavailable. This is an environment/setup guard on wasm targets, indicating the app is not running inside a proper browser context or the web feature setup is inconsistent.

Source

Thrown at crates/bevy_app/src/schedule_runner.rs:130

                            let exe_time = end_time - start_time;
                            if exe_time < wait {
                                return Ok(Some(wait - exe_time));
                            }
                        }

                        Ok(None)
                    };

                    cfg_select! {
                        all(target_arch = "wasm32", feature = "web") => {
                            fn set_timeout(callback: &Closure<dyn FnMut()>, dur: Duration) {
                                web_sys::window()
                                    .unwrap()
                                    .set_timeout_with_callback_and_timeout_and_arguments_0(
                                        callback.as_ref().unchecked_ref(),
                                        dur.as_millis() as i32,
                                    )
                                    .expect("Should register `setTimeout`.");
                            }
                            let asap = Duration::from_millis(1);

                            let exit = Rc::new(RefCell::new(AppExit::Success));
                            let closure_exit = exit.clone();

                            let mut app = Rc::new(app);
                            let moved_tick_closure = Rc::new(RefCell::new(None));
                            let base_tick_closure = moved_tick_closure.clone();

                            let tick_app = move || {
                                let app = Rc::get_mut(&mut app).unwrap();
                                let delay = tick(app, wait);
                                match delay {
                                    Ok(delay) => set_timeout(
                                        moved_tick_closure.borrow().as_ref().unwrap(),
                                        delay.unwrap_or(asap),
                                    ),

View on GitHub (pinned to 396ca72708)

Solutions

1. Ensure the app is actually running in a browser environment (wasm32 target with the web feature enabled)
2. Enter the app through the #[bevy_main] macro / wasm runner so the browser globals are initialized
3. Verify web-sys window access is not happening in a worker or non-window context without a fallback runner

When it happens

Trigger: Thrown at crates/bevy_app/src/schedule_runner.rs:130 when the library encounters an invalid state.

Common situations: See trigger scenarios.

Understand the failure class

• Timeouts: ETIMEDOUT, deadlines, and hung requests — what actually expires when a request times out.

AI-assisted analysis of bevyengine/bevy@396ca72708 (2026-08-20). Data as JSON: /api/errors/cbe9529c754bf5b8. Report an issue: GitHub.