diff --git a/gpx-rs/Cargo.lock b/gpx-rs/Cargo.lock
index 3f49f0782..68170e416 100644
--- a/gpx-rs/Cargo.lock
+++ b/gpx-rs/Cargo.lock
@@ -104,6 +104,7 @@ name = "gpx-rs"
 version = "0.1.0"
 dependencies = [
  "chrono",
+ "js-sys",
  "quick-xml",
  "uuid",
  "wasm-bindgen",
@@ -135,9 +136,9 @@ dependencies = [
 
 [[package]]
 name = "js-sys"
-version = "0.3.103"
+version = "0.3.106"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "53b44bfcdb3f8d5837a46dae1ca9660a837176eee74a28b229bc626816589102"
+checksum = "7883d941dae510fb2d978fc3fe018c71c9e2892fd38854de3e8b92c2e5ad9cc5"
 dependencies = [
  "cfg-if",
  "futures-util",
@@ -245,6 +246,17 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "syn"
+version = "3.0.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8593e8e72159ed2257d083c7a454a85cbf854f37a0966d8d483aff8c8a3ebcee"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-ident",
+]
+
 [[package]]
 name = "unicode-ident"
 version = "1.0.24"
@@ -264,9 +276,9 @@ dependencies = [
 
 [[package]]
 name = "wasm-bindgen"
-version = "0.2.126"
+version = "0.2.129"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "4b067c0c11094aef6b7a801c1e34a26affafdf3d051dba08456b868789aaf9a4"
+checksum = "9bb54f33acc68fd454578d9820b0bde1a1a3d17aa17bb7b6595806d02886d409"
 dependencies = [
  "cfg-if",
  "once_cell",
@@ -277,9 +289,9 @@ dependencies = [
 
 [[package]]
 name = "wasm-bindgen-macro"
-version = "0.2.126"
+version = "0.2.129"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "167ce5e579f6bcf889c4f7175a8a5a585de84e8ff93976ce393efa5f2837aab1"
+checksum = "2e29d0c35b16e224a7eeb5cd2d25e3e1968fbd65604117b44d3b789d00ee8535"
 dependencies = [
  "quote",
  "wasm-bindgen-macro-support",
@@ -287,22 +299,22 @@ dependencies = [
 
 [[package]]
 name = "wasm-bindgen-macro-support"
-version = "0.2.126"
+version = "0.2.129"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f3997c7839262f4ef12cf90b818d6340c18e80f263f1a94bf157d0ec4420380e"
+checksum = "6f501a8bc3719dba86ef8ae4728879c08001bea749eb1333ac5b91e040e2a6b7"
 dependencies = [
  "bumpalo",
  "proc-macro2",
  "quote",
- "syn",
+ "syn 3.0.6",
  "wasm-bindgen-shared",
 ]
 
 [[package]]
 name = "wasm-bindgen-shared"
-version = "0.2.126"
+version = "0.2.129"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "dc1b4cb0cc549fcf58d7dfc081778139b3d283a081644e833e84682ad71cea24"
+checksum = "23f0c9c52aa7cd7d77769a4cfe2a9adb1b331f489a41d912ce14513d5ab995c6"
 dependencies = [
  "unicode-ident",
 ]
@@ -328,7 +340,7 @@ checksum = "053e2e040ab57b9dc951b72c264860db7eb3b0200ba345b4e4c3b14f67855ddf"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn",
+ "syn 2.0.118",
 ]
 
 [[package]]
@@ -339,7 +351,7 @@ checksum = "3f316c4a2570ba26bbec722032c4099d8c8bc095efccdc15688708623367e358"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn",
+ "syn 2.0.118",
 ]
 
 [[package]]
diff --git a/gpx-rs/Cargo.toml b/gpx-rs/Cargo.toml
index 6d290ddd2..b7c4c929a 100644
--- a/gpx-rs/Cargo.toml
+++ b/gpx-rs/Cargo.toml
@@ -8,6 +8,7 @@ crate-type = ["cdylib"]
 
 [dependencies]
 chrono = "0.4.45"
+js-sys = "0.3.106"
 quick-xml = "0.42.0"
 uuid = {version = "1.26.1", features = ["v4", "js"]}
 wasm-bindgen = "0.2"
diff --git a/gpx-rs/README.md b/gpx-rs/README.md
new file mode 100644
index 000000000..447671d57
--- /dev/null
+++ b/gpx-rs/README.md
@@ -0,0 +1,3 @@
+```
+wasm-pack build --target bundler
+```
diff --git a/gpx-rs/src/engine.rs b/gpx-rs/src/engine.rs
index bdee4babc..9180f825c 100644
--- a/gpx-rs/src/engine.rs
+++ b/gpx-rs/src/engine.rs
@@ -1,5 +1,6 @@
 use std::rc::Rc;
 
+use js_sys::Function;
 use uuid::Uuid;
 use wasm_bindgen::prelude::*;
 
@@ -16,21 +17,23 @@ use crate::{
 // - update separate statistics
 // - update selection
 // - update selection statistics
-// - notify UI (changed files, updated selection, new stats)
+// - notify UI through callback (changed files, updated selection, new stats)
 
 #[wasm_bindgen]
-pub struct Controller {
+pub struct Engine {
     stack: Stack,
     selection: Selection,
+    callback: Function,
 }
 
 #[wasm_bindgen]
-impl Controller {
+impl Engine {
     #[wasm_bindgen(constructor)]
-    pub fn new() -> Self {
+    pub fn new(callback: Function) -> Self {
         Self {
             stack: Default::default(),
             selection: Default::default(),
+            callback,
         }
     }
 
@@ -52,6 +55,7 @@ impl Controller {
                 true
             });
         }
+        let _ = self.callback.call1(&JsValue::NULL, &JsValue::from("done!"));
     }
 
     #[wasm_bindgen]
diff --git a/website/src/lib/controller.ts b/website/src/lib/controller.ts
deleted file mode 100644
index 2ab254432..000000000
--- a/website/src/lib/controller.ts
+++ /dev/null
@@ -1,10 +0,0 @@
-class Engine {
-    _engine: Writable<any>;
-
-    constructor() {
-        this._engine = null;
-        import('gpx-rs').then((wasm) => {
-            this._engine = new wasm.Controller();
-        });
-    }
-}
diff --git a/website/src/lib/engine.ts b/website/src/lib/engine.ts
new file mode 100644
index 000000000..95e5517ce
--- /dev/null
+++ b/website/src/lib/engine.ts
@@ -0,0 +1,22 @@
+import { writable, type Subscriber, type Writable } from 'svelte/store';
+
+class Engine {
+    _engine: Writable<any>;
+
+    constructor() {
+        this._engine = writable(null);
+        import('gpx-rs').then((wasm) => {
+            this._engine.set(new wasm.Engine(this.onUpdate));
+        });
+    }
+
+    subscribe(run: Subscriber<any>, invalidate?: () => void) {
+        return this._engine.subscribe(run, invalidate);
+    }
+
+    onUpdate(message: String) {
+        console.log('message from WASM: ' + message);
+    }
+}
+
+export const engine = new Engine();