Add worker.js file

js/worker.js

@@ -0,0 +1,25 @@
+// synchronously, using the browser, import out shim JS scripts
+importScripts('pkg/web_worker.js');
+
+// Wait for the main thread to send us the shared module/memory. Once we've got
+// it, initialize it all with the `wasm_bindgen` global we imported via
+// `importScripts`.
+//
+// After our first message all subsequent messages are an entry point to run,
+// so we just do that.
+self.onmessage = event => {
+  let initialised = wasm_bindgen(...event.data).catch(err => {
+    // Propagate to main `onerror`:
+    setTimeout(() => {
+      throw err;
+    });
+    // Rethrow to keep promise rejected and prevent execution of further commands:
+    throw err;
+  });
+
+  self.onmessage = async event => {
+    // This will queue further commands up until the module is fully initialised:
+    await initialised;
+    wasm_bindgen.child_entry_point(event.data);
+  };
+};