diff --git a/Makefile b/Makefile
index e054de9..8577615 100644
--- a/Makefile
+++ b/Makefile
@@ -8,7 +8,7 @@ build:
 
 dist: build
 	mkdir -p $(BUILD)/build
-	cp -r $(SRC)/*.html $(SRC)/term.js src/examples $(SRC)/sw.js $(BUILD)
+	cp -r $(SRC)/*.html $(SRC)/term.js src/examples $(SRC)/build/sw.js $(BUILD)
 	cp $(SRC)/build/firmware.js $(SRC)/build/simulator.js $(SRC)/build/firmware.wasm  $(BUILD)/build/
 
 watch: dist
diff --git a/src/Makefile b/src/Makefile
index 66dbdcb..f2f7de1 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -147,6 +147,7 @@ $(BUILD)/micropython.js: $(OBJ) jshal.js simulator-js
 
 simulator-js:
 	npx esbuild ./simulator.ts --bundle --outfile=$(BUILD)/simulator.js --loader:.svg=text
+	npx esbuild --define:process.env.version=$$(cat ../package.json | jq .version) ./sw.ts --bundle --outfile=$(BUILD)/sw.js
 
 include $(TOP)/py/mkrules.mk
 
diff --git a/src/sw.js b/src/sw.ts
similarity index 81%
rename from src/sw.js
rename to src/sw.ts
index 0ef355d..4aa1103 100644
--- a/src/sw.js
+++ b/src/sw.ts
@@ -1,6 +1,11 @@
-const version = "v0.0.3";
+/// <reference lib="WebWorker" />
+// Empty export required due to --isolatedModules flag in tsconfig.json
+export type {};
+declare const self: ServiceWorkerGlobalScope;
+declare const clients: Clients;
+
 const assets = ["simulator.html", "build/simulator.js", "build/firmware.js"];
-const cacheName = `simulator-${version}`;
+const cacheName = `simulator-${process.env.version}`;
 
 self.addEventListener("install", (event) => {
   console.log("Installing simulator service worker...");
diff --git a/tsconfig.json b/tsconfig.json
index 0716a2c..40888c0 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -1,7 +1,7 @@
 {
   "compilerOptions": {
     "target": "es2019",
-    "lib": ["dom", "dom.iterable", "esnext"],
+    "lib": ["dom", "dom.iterable", "esnext", "WebWorker"],
     "allowJs": true,
     "skipLibCheck": true,
     "esModuleInterop": true,