egui-web: Update web_location_hash when hash in URL changes (#1140)

egui_web/CHANGELOG.md

@@ -8,6 +8,7 @@ All notable changes to the `egui_web` integration will be noted in this file.
 * Made the WebGL painter opt-in ([#1020](https://github.com/emilk/egui/pull/1020)).
 * Fix glow failure Chrome ((#1092)[https://github.com/emilk/egui/pull/1092]).
 * Shift-scroll will now result in horizontal scrolling on all platforms ((#1136)[https://github.com/emilk/egui/pull/1136]).
+* Update `epi::IntegrationInfo::web_location_hash` on `hashchange` event ([#1140](https://github.com/emilk/egui/pull/1140)).
 
 
 ## 0.16.0 - 2021-12-29

egui_web/src/backend.rs

@@ -82,7 +82,7 @@ impl epi::backend::RepaintSignal for NeedRepaint {
 // ----------------------------------------------------------------------------
 
 pub struct AppRunner {
-    frame: epi::Frame,
+    pub(crate) frame: epi::Frame,
     egui_ctx: egui::Context,
     painter: Box<dyn Painter>,
     pub(crate) input: WebInput,

egui_web/src/lib.rs

@@ -668,6 +668,22 @@ fn install_document_events(runner_ref: &AppRunnerRef) -> Result<(), JsValue> {
         closure.forget();
     }
 
+    {
+        // hashchange
+        let runner_ref = runner_ref.clone();
+        let closure = Closure::wrap(Box::new(move || {
+            let runner_lock = runner_ref.0.lock();
+            let mut frame_lock = runner_lock.frame.lock();
+
+            // `epi::Frame::info(&self)` clones `epi::IntegrationInfo`, but we need to modify the original here
+            if let Some(web_info) = &mut frame_lock.info.web_info {
+                web_info.web_location_hash = location_hash().unwrap_or_default();
+            }
+        }) as Box<dyn FnMut()>);
+        window.add_event_listener_with_callback("hashchange", closure.as_ref().unchecked_ref())?;
+        closure.forget();
+    }
+
     Ok(())
 }