use .gz version if available (works with js, css & html files)

.htaccess

<IfModule mod_rewrite.c>
  RewriteEngine On
  RewriteCond %{HTTP:Accept-Encoding} gzip
  RewriteCond %{REQUEST_FILENAME}.gz -f
  RewriteRule (.*)$ $1.gz [L]
</IfModule>

<FilesMatch ".(js.gz)$">
  AddType text/javascript .gz
  AddEncoding x-gzip .gz
</FilesMatch>

<FilesMatch ".(css.gz)$">
  AddType text/css .gz
  AddEncoding x-gzip .gz
</FilesMatch>

<FilesMatch ".(html.gz)$">
  AddType text/html .gz
  AddEncoding x-gzip .gz
</FilesMatch>

I use gulp-gzip to generate the .gz-files