fall back to gzip when zopfli compression is unavailable

config/webpack.config.js

@@ -18,6 +18,15 @@ var DEV_SERVER_LIVERELOAD = process.env.DEV_SERVER_LIVERELOAD !== 'false';
 var WEBPACK_REPORT = process.env.WEBPACK_REPORT;
 var NO_COMPRESSION = process.env.NO_COMPRESSION;
 
+// optional dependency `node-zopfli` is unavailable on CentOS 6
+var ZOPFLI_AVAILABLE;
+try {
+  require.resolve('node-zopfli');
+  ZOPFLI_AVAILABLE = true;
+} catch(err) {
+  ZOPFLI_AVAILABLE = false;
+}
+
 var config = {
   // because sqljs requires fs.
   node: {
@@ -222,7 +231,7 @@ if (IS_PRODUCTION) {
     config.plugins.push(
       new CompressionPlugin({
         asset: '[path].gz[query]',
-        algorithm: 'zopfli',
+        algorithm: ZOPFLI_AVAILABLE ? 'zopfli' : 'gzip',
       })
     );
   }