middleware.js

module.exports = function (settings) {
    settings = config(settings);
    settings.store = new MayflyStore(settings);
    
    var sessionMiddleware = session(settings);
    
    return function(req, res, next) {
      
      return sessionMiddleware(function(err) {
        if (err) {
          return next(err);
        }
        
        res.end = function() {
          ...
        }
        
        return next();
      });
    };
};

Please what language is this?