diff --git a/eframe/src/epi.rs b/eframe/src/epi.rs
index a5b32d7d..4bc54f3f 100644
--- a/eframe/src/epi.rs
+++ b/eframe/src/epi.rs
@@ -6,6 +6,9 @@
 
 #![warn(missing_docs)] // Let's keep `epi` well-documented.
 
+#[cfg(target_arch = "wasm32")]
+use std::any::Any;
+
 /// This is how your app is created.
 ///
 /// You can use the [`CreationContext`] to setup egui, restore state, setup OpenGL things, etc.
@@ -49,6 +52,15 @@ pub trait App {
     /// To force a repaint, call [`egui::Context::request_repaint`] at any time (e.g. from another thread).
     fn update(&mut self, ctx: &egui::Context, frame: &mut Frame);
 
+    // Handle to the app.
+    //
+    // Can be used from web to interact or other external context
+    // Implementation is needed, because downcasting Box<dyn App> -> Box<dyn Any> to get &ConcreteApp is not simple in current rust.
+    //
+    // Just return &mut *self
+    #[cfg(target_arch = "wasm32")]
+    fn as_any_mut(&mut self) -> &mut dyn Any;
+
     /// Called on shutdown, and perhaps at regular intervals. Allows you to save state.
     ///
     /// Only called when the "persistence" feature is enabled.
diff --git a/eframe/src/web/backend.rs b/eframe/src/web/backend.rs
index 7c1a37a6..29eebd25 100644
--- a/eframe/src/web/backend.rs
+++ b/eframe/src/web/backend.rs
@@ -35,7 +35,7 @@ impl WebInput {
 
 // ----------------------------------------------------------------------------
 
-use std::sync::atomic::Ordering::SeqCst;
+use std::{any::Any, sync::atomic::Ordering::SeqCst};
 
 /// Stores when to do the next repaint.
 pub struct NeedRepaint(Mutex<f64>);
@@ -265,6 +265,10 @@ impl AppRunner {
         &self.egui_ctx
     }
 
+    pub fn get_app_mut(&mut self) -> &mut dyn Any {
+        self.app.as_any_mut()
+    }
+
     pub fn auto_save(&mut self) {
         let now = now_sec();
         let time_since_last_save = now - self.last_save_time;
diff --git a/egui_demo_app/src/apps/custom3d_glow.rs b/egui_demo_app/src/apps/custom3d_glow.rs
index 9798dc15..3adcead5 100644
--- a/egui_demo_app/src/apps/custom3d_glow.rs
+++ b/egui_demo_app/src/apps/custom3d_glow.rs
@@ -1,5 +1,8 @@
 use std::sync::Arc;
 
+#[cfg(target_arch = "wasm32")]
+use core::any::Any;
+
 use eframe::egui_glow;
 use egui::mutex::Mutex;
 use egui_glow::glow;
@@ -49,6 +52,11 @@ impl eframe::App for Custom3d {
             self.rotating_triangle.lock().destroy(gl);
         }
     }
+
+    #[cfg(target_arch = "wasm32")]
+    fn as_any_mut(&mut self) -> &mut dyn Any {
+        &mut *self
+    }
 }
 
 impl Custom3d {
diff --git a/egui_demo_app/src/apps/custom3d_wgpu.rs b/egui_demo_app/src/apps/custom3d_wgpu.rs
index d868a57b..ebb84adf 100644
--- a/egui_demo_app/src/apps/custom3d_wgpu.rs
+++ b/egui_demo_app/src/apps/custom3d_wgpu.rs
@@ -1,5 +1,8 @@
 use std::sync::Arc;
 
+#[cfg(target_arch = "wasm32")]
+use core::any::Any;
+
 use eframe::{
     egui_wgpu::{self, wgpu},
     wgpu::util::DeviceExt,
@@ -117,6 +120,11 @@ impl eframe::App for Custom3d {
                 });
         });
     }
+
+    #[cfg(target_arch = "wasm32")]
+    fn as_any_mut(&mut self) -> &mut dyn Any {
+        &mut *self
+    }
 }
 
 impl Custom3d {
diff --git a/egui_demo_app/src/apps/http_app.rs b/egui_demo_app/src/apps/http_app.rs
index df92e748..69648080 100644
--- a/egui_demo_app/src/apps/http_app.rs
+++ b/egui_demo_app/src/apps/http_app.rs
@@ -1,6 +1,9 @@
 use egui_extras::RetainedImage;
 use poll_promise::Promise;
 
+#[cfg(target_arch = "wasm32")]
+use core::any::Any;
+
 struct Resource {
     /// HTTP response
     response: ehttp::Response,
@@ -106,6 +109,11 @@ impl eframe::App for HttpApp {
             }
         });
     }
+
+    #[cfg(target_arch = "wasm32")]
+    fn as_any_mut(&mut self) -> &mut dyn Any {
+        &mut *self
+    }
 }
 
 fn ui_url(ui: &mut egui::Ui, frame: &mut eframe::Frame, url: &mut String) -> bool {
diff --git a/egui_demo_app/src/lib.rs b/egui_demo_app/src/lib.rs
index 8ae3f422..ed9a8732 100644
--- a/egui_demo_app/src/lib.rs
+++ b/egui_demo_app/src/lib.rs
@@ -43,6 +43,25 @@ impl WebHandle {
 
         res
     }
+
+    // helper for mutating original app from javascript
+    fn with_app<F>(&mut self, func: F) -> ()
+    where
+        F: Fn(&mut WrapApp) -> (),
+    {
+        let mut runner_ref = self.handle.lock();
+        let app_ref = runner_ref.get_app_mut();
+        let app = app_ref.downcast_mut::<WrapApp>().unwrap();
+        func(app);
+    }
+
+    #[wasm_bindgen]
+    #[cfg(target_arch = "wasm32")]
+    pub fn set_some_content_from_javasript(&mut self, _some_data: &str) {
+        self.with_app(|_app| {
+            // app.data = some_data;
+        });
+    }
 }
 
 #[cfg(target_arch = "wasm32")]
diff --git a/egui_demo_app/src/wrap_app.rs b/egui_demo_app/src/wrap_app.rs
index 1a844b96..b1078d64 100644
--- a/egui_demo_app/src/wrap_app.rs
+++ b/egui_demo_app/src/wrap_app.rs
@@ -3,6 +3,9 @@ use egui_demo_lib::is_mobile;
 #[cfg(feature = "glow")]
 use eframe::glow;
 
+#[cfg(target_arch = "wasm32")]
+use core::any::Any;
+
 #[derive(Default)]
 #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
 struct EasyMarkApp {
@@ -13,6 +16,11 @@ impl eframe::App for EasyMarkApp {
     fn update(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
         self.editor.panels(ctx);
     }
+
+    #[cfg(target_arch = "wasm32")]
+    fn as_any_mut(&mut self) -> &mut dyn Any {
+        &mut *self
+    }
 }
 
 // ----------------------------------------------------------------------------
@@ -27,6 +35,11 @@ impl eframe::App for DemoApp {
     fn update(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
         self.demo_windows.ui(ctx);
     }
+
+    #[cfg(target_arch = "wasm32")]
+    fn as_any_mut(&mut self) -> &mut dyn Any {
+        &mut *self
+    }
 }
 
 // ----------------------------------------------------------------------------
@@ -46,6 +59,11 @@ impl eframe::App for FractalClockApp {
                     .ui(ui, Some(crate::seconds_since_midnight()));
             });
     }
+
+    #[cfg(target_arch = "wasm32")]
+    fn as_any_mut(&mut self) -> &mut dyn Any {
+        &mut *self
+    }
 }
 
 // ----------------------------------------------------------------------------
@@ -70,6 +88,11 @@ impl eframe::App for ColorTestApp {
             });
         });
     }
+
+    #[cfg(target_arch = "wasm32")]
+    fn as_any_mut(&mut self) -> &mut dyn Any {
+        &mut *self
+    }
 }
 
 // ----------------------------------------------------------------------------
@@ -214,6 +237,11 @@ impl eframe::App for WrapApp {
     fn on_exit(&mut self, gl: Option<&glow::Context>) {
         self.custom3d.on_exit(gl);
     }
+
+    #[cfg(target_arch = "wasm32")]
+    fn as_any_mut(&mut self) -> &mut dyn Any {
+        &mut *self
+    }
 }
 
 impl WrapApp {
diff --git a/examples/custom_3d_three-d/src/main.rs b/examples/custom_3d_three-d/src/main.rs
index 0ca9eb58..437d3548 100644
--- a/examples/custom_3d_three-d/src/main.rs
+++ b/examples/custom_3d_three-d/src/main.rs
@@ -47,6 +47,11 @@ impl eframe::App for MyApp {
             });
         });
     }
+
+    #[cfg(target_arch = "wasm32")]
+    fn as_any_mut(&mut self) -> &mut dyn Any {
+        &mut *self
+    }
 }
 
 impl MyApp {