Graceful exit from web (#1650)

Return a handle that can be used to stop a running egui instance.

egui_demo_app/src/lib.rs

@@ -5,6 +5,15 @@ mod backend_panel;
 pub(crate) mod frame_history;
 mod wrap_app;
 
+#[cfg(target_arch = "wasm32")]
+use std::sync::Arc;
+
+#[cfg(target_arch = "wasm32")]
+use eframe::web::AppRunner;
+
+#[cfg(target_arch = "wasm32")]
+use egui::mutex::Mutex;
+
 pub use wrap_app::WrapApp;
 
 /// Time of day as seconds since midnight. Used for clock in demo app.
@@ -19,23 +28,60 @@ pub(crate) fn seconds_since_midnight() -> f64 {
 #[cfg(target_arch = "wasm32")]
 use eframe::wasm_bindgen::{self, prelude::*};
 
+#[cfg(target_arch = "wasm32")]
+#[wasm_bindgen]
+pub struct WebHandle {
+    handle: Arc<Mutex<AppRunner>>,
+}
+
+#[cfg(target_arch = "wasm32")]
+#[wasm_bindgen]
+impl WebHandle {
+    #[wasm_bindgen]
+    #[cfg(target_arch = "wasm32")]
+    pub fn stop_web(&self) -> Result<(), wasm_bindgen::JsValue> {
+        let mut app = self.handle.lock();
+        let res = app.destroy();
+
+        // let numw = Arc::weak_count(&app);
+        // let nums = Arc::strong_count(&app);
+        // tracing::debug!("runner ref {:?}, {:?}", numw, nums);
+
+        res
+    }
+}
+
+#[cfg(target_arch = "wasm32")]
+#[wasm_bindgen]
+pub fn init_wasm_hooks() {
+    // Make sure panics are logged using `console.error`.
+    console_error_panic_hook::set_once();
+
+    // Redirect tracing to console.log and friends:
+    tracing_wasm::set_as_global_default();
+}
+
+#[cfg(target_arch = "wasm32")]
+#[wasm_bindgen]
+pub fn start_separate(canvas_id: &str) -> Result<WebHandle, wasm_bindgen::JsValue> {
+    let web_options = eframe::WebOptions::default();
+    let handle = eframe::start_web(
+        canvas_id,
+        web_options,
+        Box::new(|cc| Box::new(WrapApp::new(cc))),
+    )
+    .map(|handle| WebHandle { handle });
+
+    handle
+}
+
 /// This is the entry-point for all the web-assembly.
 /// This is called once from the HTML.
 /// It loads the app, installs some callbacks, then returns.
 /// You can add more callbacks like this if you want to call in to your code.
 #[cfg(target_arch = "wasm32")]
 #[wasm_bindgen]
-pub fn start(canvas_id: &str) -> Result<(), wasm_bindgen::JsValue> {
-    // Make sure panics are logged using `console.error`.
-    console_error_panic_hook::set_once();
-
-    // Redirect tracing to console.log and friends:
-    tracing_wasm::set_as_global_default();
-
-    let web_options = eframe::WebOptions::default();
-    eframe::start_web(
-        canvas_id,
-        web_options,
-        Box::new(|cc| Box::new(WrapApp::new(cc))),
-    )
+pub fn start(canvas_id: &str) -> Result<WebHandle, wasm_bindgen::JsValue> {
+    init_wasm_hooks();
+    start_separate(canvas_id)
 }