code: function webpackDev(app) {
  
    var { config } = app.locals;
  
    // configure data-source
    var DataSource = require('loopback-datasource-juggler').DataSource;
    var mainDs = new DataSource(config.db);
  
    // Enable All CORS Requests
    app.use(cors());
  
    let sql = "SELECT * FROM zlSite WHERE zsTheme != ''";
    mainDs.connector.execute(sql, [null], function (err, zs) {
      if (err) app.error(err);
      else {
        _.forEach(zs, function(zlSite) {
          // check if we're only working on 1 site
          if (process.env.DEV_SITE && zlSite.zsId !== process.env.DEV_SITE) {
            return;
          }
  
          // webpack config specific for hot/webpackDevServer
          let hotConf = {
            output: {
              filename: `${zlSite.zsId}/dist/js/[name].js`,
              publicPath: '/',
              path: '/'
            },
            devtool: 'cheap-module-source-map',
            plugins: [
              new ExtractTextPlugin({ filename: `${zlSite.zsId}/dist/css/[name].css` })
            ]
          }
  
          // make bundle config for site
          readyBundle(app, zlSite, '', '', (wpConfig) => {
            var webpackConfig = merge(common, wpConfig, hotConf);
            var compiler = webpack(webpackConfig);
  
            app.use(webpackDevMiddleware(compiler, {
              publicPath: "/",
              lazy: false
            }));
          });
        });
  
        // launch webpack-dev-middleware server
        var port = 3000
        if (config.webpackDevServer && config.webpackDevServer.port) {
          port = config.webpackDevServer.port;
        }
        app.listen(port, function () {
          app.debug('webpackDevMiddleware Listening on port %s!', port)
        });
      }
    });
  }
docs: dev/bundle only mode