diff --git a/docs/sw.js b/docs/sw.js
new file mode 100644
index 0000000..eef3c08
--- /dev/null
+++ b/docs/sw.js
@@ -0,0 +1 @@
+importScripts('https://cdn.jsdelivr.net/gh/nlepage/go-wasm-http-server@b4be701615d284296a4a1aaa852db02f139969ee/index.js')
diff --git a/index.js b/index.js
index b8ba0f5..c2464fa 100644
--- a/index.js
+++ b/index.js
@@ -1,7 +1,5 @@
-const swUrl = 'https://cdn.jsdelivr.net/gh/nlepage/go-wasm-http-server@b4be701615d284296a4a1aaa852db02f139969ee/index.js'
-
 window.wasmhttp = {
-  register: async (wasm, { scope, base = '' } = {}) => {
+  register: async (wasm, { scope, base = '', swUrl = 'sw.js' } = {}) => {
     const options = {}
     if (scope) options.scope = scope
     //FIXME register once