diff --git a/app/models/javascript_cache.rb b/app/models/javascript_cache.rb
index 20f8b63a846..b92509bb892 100644
--- a/app/models/javascript_cache.rb
+++ b/app/models/javascript_cache.rb
@@ -8,11 +8,19 @@ class JavascriptCache < ActiveRecord::Base
   before_save :update_digest
 
   def url
-    "#{GlobalSetting.cdn_url}#{Discourse.base_path}/theme-javascripts/#{digest}.js?__ws=#{Discourse.current_hostname}"
+    "#{GlobalSetting.cdn_url}#{Discourse.base_path}#{path}"
+  end
+
+  def local_url
+    "#{Discourse.base_url}#{path}"
   end
 
   private
 
+  def path
+    "/theme-javascripts/#{digest}.js?__ws=#{Discourse.current_hostname}"
+  end
+
   def update_digest
     self.digest = Digest::SHA1.hexdigest(content) if content_changed?
   end
diff --git a/app/models/theme.rb b/app/models/theme.rb
index b2d867509c9..990b39c1e85 100644
--- a/app/models/theme.rb
+++ b/app/models/theme.rb
@@ -539,12 +539,19 @@ class Theme < ActiveRecord::Base
     end
 
     theme_uploads = {}
+    theme_uploads_local = {}
+
     upload_fields.each do |field|
       if field.upload&.url
         theme_uploads[field.name] = Discourse.store.cdn_url(field.upload.url)
       end
+      if field.javascript_cache
+        theme_uploads_local[field.name] = field.javascript_cache.local_url
+      end
     end
+
     hash['theme_uploads'] = theme_uploads if theme_uploads.present?
+    hash['theme_uploads_local'] = theme_uploads_local if theme_uploads_local.present?
 
     hash
   end
@@ -652,7 +659,7 @@ class Theme < ActiveRecord::Base
     end
 
     settings_hash&.each do |name, value|
-      next if name == "theme_uploads"
+      next if name == "theme_uploads" || name == "theme_uploads_local"
       contents << to_scss_variable(name, value)
     end
 
diff --git a/app/models/theme_field.rb b/app/models/theme_field.rb
index 22c03f61728..0e3c8663f3a 100644
--- a/app/models/theme_field.rb
+++ b/app/models/theme_field.rb
@@ -184,7 +184,7 @@ class ThemeField < ActiveRecord::Base
 
     begin
       content = File.read(path)
-      svg_file = Nokogiri::XML(content) do |config|
+      Nokogiri::XML(content) do |config|
         config.options = Nokogiri::XML::ParseOptions::NOBLANKS
       end
     rescue => e
@@ -568,6 +568,12 @@ class ThemeField < ActiveRecord::Base
     if (will_save_change_to_value? || will_save_change_to_upload_id?) && !will_save_change_to_value_baked?
       self.value_baked = nil
     end
+    if upload && upload.extension == "js"
+      if will_save_change_to_upload_id? || !javascript_cache
+        javascript_cache ||= build_javascript_cache
+        javascript_cache.content = upload.content
+      end
+    end
   end
 
   after_save do
diff --git a/app/models/upload.rb b/app/models/upload.rb
index 061cc266af3..b24044b7a68 100644
--- a/app/models/upload.rb
+++ b/app/models/upload.rb
@@ -171,6 +171,22 @@ class Upload < ActiveRecord::Base
     end
   end
 
+  def content
+    original_path = Discourse.store.path_for(self)
+    external_copy = nil
+
+    if original_path.blank?
+      external_copy = Discourse.store.download(self)
+      original_path = external_copy.path
+    end
+
+    File.read(original_path)
+  ensure
+    if external_copy
+      File.unlink(external_copy.path)
+    end
+  end
+
   def fix_image_extension
     return false if extension == "unknown"
 
diff --git a/config/site_settings.yml b/config/site_settings.yml
index 9ebfb5efa25..78ab66041c1 100644
--- a/config/site_settings.yml
+++ b/config/site_settings.yml
@@ -1274,7 +1274,7 @@ files:
     default: 50000
     max: 1024000
   theme_authorized_extensions:
-    default: "jpg|jpeg|png|woff|woff2|svg|eot|ttf|otf|gif|webp|js"
+    default: "wasm|jpg|jpeg|png|woff|woff2|svg|eot|ttf|otf|gif|webp|js"
     type: list
     list_type: compact
   authorized_extensions:
diff --git a/lib/svg_sprite/svg_sprite.rb b/lib/svg_sprite/svg_sprite.rb
index 634937f0cc1..d7b5ebb0bcd 100644
--- a/lib/svg_sprite/svg_sprite.rb
+++ b/lib/svg_sprite/svg_sprite.rb
@@ -237,24 +237,7 @@ module SvgSprite
 
       custom_sprite_paths = Dir.glob(plugin_paths)
 
-      if theme_id.present?
-        ThemeField.where(type_id: ThemeField.types[:theme_upload_var], name: THEME_SPRITE_VAR_NAME, theme_id: Theme.transform_ids(theme_id))
-          .pluck(:upload_id).each do |upload_id|
-
-          upload = Upload.find(upload_id) rescue nil
-
-          if Discourse.store.external?
-            external_copy = Discourse.store.download(upload) rescue nil
-            original_path = external_copy.try(:path)
-          else
-            original_path = Discourse.store.path_for(upload)
-          end
-
-          custom_sprite_paths << original_path if original_path.present?
-        end
-      end
-
-      custom_sprite_paths.map do |path|
+      custom_sprites = custom_sprite_paths.map do |path|
         if File.exist?(path)
           {
             filename: "#{File.basename(path, ".svg")}",
@@ -262,6 +245,25 @@ module SvgSprite
           }
         end
       end
+
+      if theme_id.present?
+        ThemeField.where(type_id: ThemeField.types[:theme_upload_var], name: THEME_SPRITE_VAR_NAME, theme_id: Theme.transform_ids(theme_id))
+          .pluck(:upload_id, :theme_id).each do |upload_id, child_theme_id|
+
+          begin
+            upload = Upload.find(upload_id)
+            custom_sprites << {
+              filename: "theme_#{theme_id}_#{upload_id}.svg",
+              sprite: upload.content
+            }
+          rescue => e
+            name = Theme.find(child_theme_id).name rescue nil
+            Discourse.warn_exception(e, "#{name} theme contains a corrupt svg upload")
+          end
+
+        end
+      end
+      custom_sprites
     end
   end
 
@@ -483,7 +485,7 @@ License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL
 
     # Need to load full records for default values
     Theme.where(id: theme_ids).each do |theme|
-      settings = theme.cached_settings.each do |key, value|
+      _settings = theme.cached_settings.each do |key, value|
         if key.to_s.include?("_icon") && String === value
           theme_icon_settings |= value.split('|')
         end
diff --git a/lib/theme_store/git_importer.rb b/lib/theme_store/git_importer.rb
index 409a39eca49..6ef40d2c16f 100644
--- a/lib/theme_store/git_importer.rb
+++ b/lib/theme_store/git_importer.rb
@@ -110,7 +110,7 @@ class ThemeStore::GitImporter
       else
         Discourse::Utils.execute_command(git_ssh_command, "git", "clone", @url, @temp_folder)
       end
-    rescue RuntimeError => err
+    rescue RuntimeError
       raise RemoteTheme::ImportError.new(I18n.t("themes.import_error.git"))
     end
   ensure
diff --git a/lib/theme_store/zip_exporter.rb b/lib/theme_store/zip_exporter.rb
index edc8639f8a5..ed1d64c187d 100644
--- a/lib/theme_store/zip_exporter.rb
+++ b/lib/theme_store/zip_exporter.rb
@@ -53,8 +53,7 @@ class ThemeStore::ZipExporter
       raise RuntimeError.new("Theme exporter tried to leave directory") unless path.to_s.starts_with?(destination_folder)
 
       if ThemeField.types[field.type_id] == :theme_upload_var
-        filename = Discourse.store.path_for(field.upload)
-        content = filename ? File.read(filename) : Discourse.store.download(field.upload).read
+        content = field.upload.content
       else
         content = field.value
       end
diff --git a/spec/lib/svg_sprite/svg_sprite_spec.rb b/spec/lib/svg_sprite/svg_sprite_spec.rb
index 423c144c7a5..b72829af999 100644
--- a/spec/lib/svg_sprite/svg_sprite_spec.rb
+++ b/spec/lib/svg_sprite/svg_sprite_spec.rb
@@ -213,7 +213,7 @@ describe SvgSprite do
   end
 
   it "includes Font Awesome icon from groups" do
-    group = Fabricate(:group, flair_icon: "far-building")
+    _group = Fabricate(:group, flair_icon: "far-building")
     expect(SvgSprite.bundle).to match(/far-building/)
   end
 
diff --git a/spec/models/theme_field_spec.rb b/spec/models/theme_field_spec.rb
index 7fc6eacc3ee..ad43c0d1e09 100644
--- a/spec/models/theme_field_spec.rb
+++ b/spec/models/theme_field_spec.rb
@@ -174,7 +174,7 @@ HTML
 
   it "correctly handles extra JS fields" do
     js_field = theme.set_field(target: :extra_js, name: "discourse/controllers/discovery.js.es6", value: "import 'discourse/lib/ajax'; console.log('hello from .js.es6');")
-    js_2_field = theme.set_field(target: :extra_js, name: "discourse/controllers/discovery-2.js", value: "import 'discourse/lib/ajax'; console.log('hello from .js');")
+    _js_2_field = theme.set_field(target: :extra_js, name: "discourse/controllers/discovery-2.js", value: "import 'discourse/lib/ajax'; console.log('hello from .js');")
     hbs_field = theme.set_field(target: :extra_js, name: "discourse/templates/discovery.hbs", value: "{{hello-world}}")
     raw_hbs_field = theme.set_field(target: :extra_js, name: "discourse/templates/discovery.hbr", value: "{{hello-world}}")
     hbr_field = theme.set_field(target: :extra_js, name: "discourse/templates/other_discovery.hbr", value: "{{hello-world}}")
@@ -429,4 +429,90 @@ HTML
     end
   end
 
+  context 'local js assets' do
+
+    let :js_content do
+      "// not transpiled; console.log('hello world');"
+    end
+
+    let :upload_file do
+      tmp = Tempfile.new(["jsfile", ".js"])
+      File.write(tmp.path, js_content)
+      tmp
+    end
+
+    after do
+      upload_file.unlink
+    end
+
+    it "correctly handles local JS asset caching" do
+
+      upload = UploadCreator.new(upload_file, "test.js", for_theme: true)
+        .create_for(Discourse::SYSTEM_USER_ID)
+
+      js_field = theme.set_field(
+        target: :common,
+        type_id: ThemeField.types[:theme_upload_var],
+        name: 'test_js',
+        upload_id: upload.id
+      )
+
+      common_field = theme.set_field(
+        target: :common,
+        name: "head_tag",
+        value: "<script>let c = 'd';</script>",
+        type: :html
+      )
+
+      theme.set_field(
+        target: :settings,
+        type: :yaml,
+        name: "yaml",
+        value: "hello: world"
+      )
+
+      theme.set_field(
+        target: :extra_js,
+        name: "discourse/controllers/discovery.js.es6",
+        value: "import 'discourse/lib/ajax'; console.log('hello from .js.es6');"
+      )
+
+      theme.save!
+
+      # a bit fragile, but at least we test it properly
+      [theme.reload.javascript_cache.content, common_field.reload.javascript_cache.content].each do |js|
+        js_to_eval = <<~JS
+          var settings;
+          var window = {};
+          var require = function(name) {
+            if(name == "discourse/lib/theme-settings-store") {
+              return({
+                registerSettings: function(id, s) {
+                  settings = s;
+                }
+              });
+            }
+          }
+          window.require = require;
+          #{js}
+          settings
+        JS
+
+        ctx = MiniRacer::Context.new
+        val = ctx.eval(js_to_eval)
+        ctx.dispose
+
+        expect(val["theme_uploads"]["test_js"]).to eq(js_field.upload.url)
+        expect(val["theme_uploads_local"]["test_js"]).to eq(js_field.javascript_cache.local_url)
+
+      end
+
+      # this is important, we do not want local_js_urls to leak into scss
+      expect(theme.scss_variables).to include("$hello: unquote(\"world\");")
+      expect(theme.scss_variables).to include("$test_js: unquote(\"#{upload.url}\");")
+
+      expect(theme.scss_variables).not_to include("theme_uploads")
+    end
+  end
+
 end
diff --git a/spec/models/upload_spec.rb b/spec/models/upload_spec.rb
index f15dd8c8aeb..69c2e54177f 100644
--- a/spec/models/upload_spec.rb
+++ b/spec/models/upload_spec.rb
@@ -204,6 +204,13 @@ describe Upload do
         setup_s3
       end
 
+      it "can download an s3 upload" do
+        stub_request(:get, upload.url)
+          .to_return(status: 200, body: "hello", headers: {})
+
+        expect(upload.content).to eq("hello")
+      end
+
       it "should return the right upload when using base url (not CDN) for s3" do
         upload
         expect(Upload.get_from_url(upload.url)).to eq(upload)