diff --git a/app/assets/javascripts/service-worker.js.erb b/app/assets/javascripts/service-worker.js.erb
index a2df90a5064..1d889322894 100644
--- a/app/assets/javascripts/service-worker.js.erb
+++ b/app/assets/javascripts/service-worker.js.erb
@@ -7,7 +7,7 @@ workbox.setConfig({
   debug: false
 });
 
-const cacheVersion = "1";
+var cacheVersion = "1";
 
 // Cache all GET requests, so Discourse can be used while offline
 workbox.routing.registerRoute(
@@ -24,7 +24,7 @@ workbox.routing.registerRoute(
   })
 );
 
-const idleThresholdTime = 1000 * 10; // 10 seconds
+var idleThresholdTime = 1000 * 10; // 10 seconds
 var lastAction = -1;
 
 function isIdle() {
diff --git a/lib/tasks/assets.rake b/lib/tasks/assets.rake
index 4a02d5f1b10..7625fece589 100644
--- a/lib/tasks/assets.rake
+++ b/lib/tasks/assets.rake
@@ -78,7 +78,15 @@ def compress_node(from, to)
   source_map_root = assets + ((d = File.dirname(from)) == "." ? "" : "/#{d}")
   source_map_url = cdn_path "/assets/#{to}.map"
 
-  cmd = "uglifyjs '#{assets_path}/#{from}' -p relative -m -c -o '#{to_path}' --source-map-root '#{source_map_root}' --source-map '#{assets_path}/#{to}.map' --source-map-url '#{source_map_url}'"
+  cmd = if `uglifyjs -V`.match?(/2(.\d*){2}/)
+    <<~EOS
+    uglifyjs '#{assets_path}/#{from}' -p relative -m -c -o '#{to_path}' --source-map-root '#{source_map_root}' --source-map '#{assets_path}/#{to}.map' --source-map-url '#{source_map_url}'
+    EOS
+  else
+    <<~EOS
+    uglifyjs '#{assets_path}/#{from}' -m -c -o '#{to_path}' --source-map "root='#{source_map_root}',url='#{source_map_url}'" --output '#{to_path}'
+    EOS
+  end
 
   STDERR.puts cmd
   result = `#{cmd} 2>&1`
diff --git a/vendor/assets/javascripts/caret_position.js b/vendor/assets/javascripts/caret_position.js
index ea84372906b..2393c6f4068 100644
--- a/vendor/assets/javascripts/caret_position.js
+++ b/vendor/assets/javascripts/caret_position.js
@@ -69,7 +69,7 @@ $.fn.caretPosition = function(options) {
   clone = $("<div><p></p></div>").appendTo("body");
   p = clone.find("p");
 
-  const isRTL = $("html").hasClass("rtl");
+  var isRTL = $("html").hasClass("rtl");
   clone.css({
     border: "1px solid black",
     padding: important("padding"),