diff --git a/src/index.js b/src/index.js
index c679b42..9f0f2be 100644
--- a/src/index.js
+++ b/src/index.js
@@ -12,63 +12,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-import {
-  ScrollTimeline,
-  ViewTimeline,
-} from "./scroll-timeline-base";
-import {
-  animate,
-  elementGetAnimations,
-  documentGetAnimations,
-  ProxyAnimation
-} from "./proxy-animation.js";
-
 import { initCSSPolyfill } from "./scroll-timeline-css"
-
-function initJSPolyfill() {
-  // Don’t load if the browser already has support
-  if ((typeof window.ScrollTimeline) !== 'undefined') {
-    return false;
-  }
-
-  if (
-    !Reflect.defineProperty(window, 'ScrollTimeline', { value: ScrollTimeline })
-  ) {
-    throw Error(
-      'Error installing ScrollTimeline polyfill: could not attach ScrollTimeline to window'
-    );
-  }
-  if (
-    !Reflect.defineProperty(window, 'ViewTimeline', { value: ViewTimeline })
-  ) {
-    throw Error(
-      'Error installing ViewTimeline polyfill: could not attach ViewTimeline to window'
-    );
-  }
-
-  if (
-    !Reflect.defineProperty(Element.prototype, 'animate', { value: animate })
-  ) {
-    throw Error(
-      "Error installing ScrollTimeline polyfill: could not attach WAAPI's animate to DOM Element"
-    );
-  }
-  if (!Reflect.defineProperty(window, 'Animation', { value: ProxyAnimation })) {
-    throw Error('Error installing Animation constructor.');
-  }
-  if (!Reflect.defineProperty(Element.prototype, "getAnimations", { value: elementGetAnimations })) {
-    throw Error(
-      "Error installing ScrollTimeline polyfill: could not attach WAAPI's getAnimations to DOM Element"
-    );
-  }
-  if (!Reflect.defineProperty(document, "getAnimations", { value: documentGetAnimations })) {
-    throw Error(
-      "Error installing ScrollTimeline polyfill: could not attach WAAPI's getAnimations to document"
-    );
-  }
-
-  return true;
-}
+import { initJSPolyfill } from "./scroll-timeline-js"
 
 function initPolyfill() {
   const jsPolyfillLoaded = initJSPolyfill();
diff --git a/src/scroll-timeline-js.js b/src/scroll-timeline-js.js
new file mode 100644
index 0000000..14ae62b
--- /dev/null
+++ b/src/scroll-timeline-js.js
@@ -0,0 +1,69 @@
+// Copyright 2019 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the 'License');
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an 'AS IS' BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import {
+  ScrollTimeline,
+  ViewTimeline,
+} from './scroll-timeline-base';
+import {
+  animate,
+  elementGetAnimations,
+  documentGetAnimations,
+  ProxyAnimation
+} from './proxy-animation.js';
+
+export function initJSPolyfill() {
+  // Don’t load if the browser already has support
+  if ((typeof window.ScrollTimeline) !== 'undefined') {
+    return false;
+  }
+
+  if (
+    !Reflect.defineProperty(window, 'ScrollTimeline', { value: ScrollTimeline })
+  ) {
+    throw Error(
+      'Error installing ScrollTimeline polyfill: could not attach ScrollTimeline to window'
+    );
+  }
+  if (
+    !Reflect.defineProperty(window, 'ViewTimeline', { value: ViewTimeline })
+  ) {
+    throw Error(
+      'Error installing ViewTimeline polyfill: could not attach ViewTimeline to window'
+    );
+  }
+
+  if (
+    !Reflect.defineProperty(Element.prototype, 'animate', { value: animate })
+  ) {
+    throw Error(
+      'Error installing ScrollTimeline polyfill: could not attach WAAPI’s animate to DOM Element'
+    );
+  }
+  if (!Reflect.defineProperty(window, 'Animation', { value: ProxyAnimation })) {
+    throw Error('Error installing Animation constructor.');
+  }
+  if (!Reflect.defineProperty(Element.prototype, 'getAnimations', { value: elementGetAnimations })) {
+    throw Error(
+      'Error installing ScrollTimeline polyfill: could not attach WAAPI’s getAnimations to DOM Element'
+    );
+  }
+  if (!Reflect.defineProperty(document, 'getAnimations', { value: documentGetAnimations })) {
+    throw Error(
+      'Error installing ScrollTimeline polyfill: could not attach WAAPI’s getAnimations to document'
+    );
+  }
+
+  return true;
+}
\ No newline at end of file