code: function bundleServer(app, promises) {
    var { themes, config } = app.locals;
  
    // iterate all themes
    _.forEach(themes, function(val, theme) {
      promises.push( new Promise(function(resolve) {
        // make bundle config for server-renderer
        readyBundle(app, '', theme, resolve, (wpConfig, sitePath, appBundled, done) => {
          // if wpConfig is empty that means packages was not changed, so skip
          if (!wpConfig) return;
  
          // Webpack specific for bundled file
          let conf = {
            output: {
              filename: `${config.contentPath}/build/${theme}/server-render.js`
            },
            entry: `${themes[appBundled].path}/${themes[appBundled].zealderConfig.serverRenderFile}`
          };
  
          var webpackConfig = merge(webpackServer, wpConfig, conf);
          webpack(webpackConfig, (err, stats) => {
            if (err) throw new Error(err.stack || err);
            const info = stats.toJson();
            if (stats.hasErrors()) app.error(info.errors);
            done();
          });
        });
      }));
    });
  }
docs: make server bundles