diff --git a/app/assets/javascripts/service-worker.js.erb b/app/assets/javascripts/service-worker.js.erb
index 138345daa3f..43fb85a33e6 100644
--- a/app/assets/javascripts/service-worker.js.erb
+++ b/app/assets/javascripts/service-worker.js.erb
@@ -11,7 +11,7 @@ const CURRENT_CACHES = {
 const OFFLINE_URL = 'offline.html';
 
 function createCacheBustedRequest(url) {
-  let request = new Request(url, {cache: 'reload'});
+  var request = new Request(url, {cache: 'reload'});
   // See https://fetch.spec.whatwg.org/#concept-request-mode
   // This is not yet supported in Chrome as of M48, so we need to explicitly check to see
   // if the cache: 'reload' option had any effect.
@@ -20,12 +20,12 @@ function createCacheBustedRequest(url) {
   }
 
   // If {cache: 'reload'} didn't have any effect, append a cache-busting URL parameter instead.
-  let bustedUrl = new URL(url, self.location.href);
-  bustedUrl.search += `${(bustedUrl.search ? '&' : '')}cachebust=${Date.now()}`;
+  var bustedUrl = new URL(url, self.location.href);
+  bustedUrl.search += (bustedUrl.search ? '&' : '') + 'cachebust=' + Date.now();
   return new Request(bustedUrl);
 }
 
-self.addEventListener('install', event => {
+self.addEventListener('install', function(event) {
   event.waitUntil(
     // We can't use cache.add() here, since we want OFFLINE_URL to be the cache key, but
     // the actual URL we end up requesting might include a cache-busting parameter.
@@ -37,18 +37,18 @@ self.addEventListener('install', event => {
   );
 });
 
-self.addEventListener('activate', event => {
+self.addEventListener('activate', function(event) {
   // Delete all caches that aren't named in CURRENT_CACHES.
   // While there is only one cache in this example, the same logic will handle the case where
   // there are multiple versioned caches.
-  let expectedCacheNames = Object.keys(CURRENT_CACHES).map(function(key) {
+  var expectedCacheNames = Object.keys(CURRENT_CACHES).map(function(key) {
     return CURRENT_CACHES[key];
   });
 
   event.waitUntil(
-    caches.keys().then(cacheNames => {
+    caches.keys().then(function(cacheNames) {
       return Promise.all(
-        cacheNames.map(cacheName => {
+        cacheNames.map(function(cacheName) {
           if (expectedCacheNames.indexOf(cacheName) === -1) {
             // If this cache name isn't present in the array of "expected" cache names,
             // then delete it.
@@ -60,7 +60,7 @@ self.addEventListener('activate', event => {
   );
 });
 
-self.addEventListener('fetch', event => {
+self.addEventListener('fetch', function(event) {
   // We only want to call event.respondWith() if this is a navigation request
   // for an HTML page.
   // request.mode of 'navigate' is unfortunately not supported in Chrome
@@ -70,7 +70,7 @@ self.addEventListener('fetch', event => {
       (event.request.method === 'GET' &&
        event.request.headers.get('accept').includes('text/html'))) {
     event.respondWith(
-      fetch(event.request).catch(error => {
+      fetch(event.request).catch(function(error) {
         // The catch is only triggered if fetch() throws an exception, which will most likely
         // happen due to the server being unreachable.
         // If fetch() returns a valid HTTP response with an response code in the 4xx or 5xx