diff --git a/docs/api.wasm b/docs/api.wasm
index 6d697eb..46b3538 100755
Binary files a/docs/api.wasm and b/docs/api.wasm differ
diff --git a/serve.go b/serve.go
index 56f990d..031d493 100644
--- a/serve.go
+++ b/serve.go
@@ -3,7 +3,6 @@ package wasmhttp
 import (
 	"fmt"
 	"net/http"
-	"os"
 	"strings"
 	"syscall/js"
 
@@ -17,19 +16,14 @@ func Serve(handler http.Handler) func() {
 		h = http.DefaultServeMux
 	}
 
-	var path = os.Getenv("WASMHTTP_PATH")
-	if !strings.HasSuffix(path, "/") {
-		path = path + "/"
+	var prefix = js.Global().Get("wasmhttp").Get("path").String()
+	for strings.HasSuffix(prefix, "/") {
+		prefix = strings.TrimSuffix(prefix, "/")
 	}
 
-	if path != "" { // FIXME always true since / suffix is added to path
-		var prefix = os.Getenv("WASMHTTP_PATH")
-		for strings.HasSuffix(prefix, "/") {
-			prefix = strings.TrimSuffix(prefix, "/")
-		}
-
+	if prefix != "" {
 		var mux = http.NewServeMux()
-		mux.Handle(path, http.StripPrefix(prefix, h))
+		mux.Handle(prefix+"/", http.StripPrefix(prefix, h))
 		h = mux
 	}
 
@@ -64,7 +58,7 @@ func Serve(handler http.Handler) func() {
 		return resPromise
 	})
 
-	js.Global().Get("wasmhttp").Call("registerHandler", os.Getenv("WASMHTTP_HANDLER_ID"), cb)
+	js.Global().Get("wasmhttp").Call("setHandler", cb)
 
 	return cb.Release
 }
diff --git a/sw.js b/sw.js
index c2e1927..d777926 100644
--- a/sw.js
+++ b/sw.js
@@ -1,37 +1,25 @@
 importScripts('https://cdn.jsdelivr.net/gh/golang/go@go1.15.7/misc/wasm/wasm_exec.js')
 
-let nextHandlerId = 1
-const handlerResolvers = {}
-const handlers = []
-
-self.wasmhttp = {
-  registerHandler: (handlerId, handler) => {
-    handlerResolvers[handlerId](handler)
-    delete handlerResolvers[handlerId]
-  },
-}
-
 function registerWasmHTTPListener(wasm, base, args = []) {
   let path = new URL(registration.scope).pathname
   if (base && base !== '') path = `${trimEnd(path, '/')}/${trimStart(base, '/')}`
 
-  const wasmPromise = fetch(wasm).then(res => res.arrayBuffer())
+  const handlerPromise = new Promise(setHandler => {
+    self.wasmhttp = {
+      path,
+      setHandler,
+    }
+  })
+
+  const go = new Go()
+  go.env = { WASMHTTP_HANDLER_ID: handlerId, WASMHTTP_PATH: path }
+  go.argv = [wasm, ...args]
+  WebAssembly.instantiateStreaming(fetch(wasm), go.importObject).then(({ instance }) => go.run(instance))
 
   addEventListener('fetch', e => {
     const { pathname } = new URL(e.request.url)
     if (!pathname.startsWith(path)) return
 
-    const handlerId = `${nextHandlerId++}`
-    const handlerPromise = new Promise(resolve => handlerResolvers[handlerId] = resolve)
-
-    const go = new Go()
-    go.env = { WASMHTTP_HANDLER_ID: handlerId, WASMHTTP_PATH: path }
-    go.argv = [wasm, ...args]
-    // FIXME await ? catch ?
-    wasmPromise
-      .then(wasm => WebAssembly.instantiate(wasm, go.importObject))
-      .then(({ instance }) => go.run(instance))
-
     e.respondWith(handlerPromise.then(handler => handler(e.request)))
   })
 }