Express is a minimal and flexible node.js web application framework, providing a robust set of features for building single and multi-page, and hybrid web applications.

On 9th April, 2014, new version 4.0 of Express web application framework has been released. There are some significant changes which you should be aware of before switching to the latest version.

Express generation

The express command has been moved to quickstart project generator express-generator. You can find more about the new module here.

Node 0.8.x support

Express 4.0 does not support Node 0.8.x any more. That might be an issue if you use any modules which require Node 0.8.x.


The conditionally invoked callback configuration method: app.configure() has been removed. In version 4.0 if statements should be used instead e.g.

Version 3.x

// all environments
  app.set('title', 'Application Title');

// development only
app.configure('development', function(){
  app.set('mongodb_uri', 'mongo://localhost/dev');

// production only
app.configure('production', function(){
  app.set('mongodb_uri', 'mongo://localhost/prod');

Version 4.0

// all environments
app.set('title', 'Application Title');

// development only
if ('development' == app.get('env')) {
  app.set('mongodb_uri', 'mongo://localhost/dev');

// production only
if ('production' == app.get('env')) {
  app.set('mongodb_uri', 'mongo://localhost/prod');

Removed Bundled Middleware

All bundled middleware except express.static() has been moved into separate repository - expressjs. So as of 4.x, Express no longer depends on Connect module.

A list of middleware modules supported by the Connect/Express team:

Express 3.x Module Module Replacement for Express 4.x
bodyParser body-parser
json body-parser
urlencoded body-parser
compress compression
timeout connect-timeout
cookieParser cookie-parser
cookieSession cookie-session
csrf csurf
error-handler errorhandler
session express-session
method-override method-override
logger morgan
response-time response-time
directory serve-index
static serve-static
favicon static-favicon
vhost vhost

Note that some middleware modules previously included with Connect are no longer supported by the Connect/Express team. You can refer to http-framework GitHub project for other compatibil middleware modules.

Checkout here for more module alternatives.

Routing changes

Approach to routing has been improved. New changes give developer more control and more robust solution for building bespoke routes.

New app.route() has been added as a shortcut to the Router. Using app.route() is a recommended approach to avoiding duplicate route naming and thus typo errors e.g.

var app = express();

    .all(function(req, res, next) {
        // Perform some operations common to login page rendering and loggin operation
    .get(function(req, res, next) {
        res.render(...);  // render login page
    .post(function(req, res, next) {
        // Perform login operation i.e. user name & password check etc.

Router API has been added. A router is an isolated instance of middleware and routes. We are able to add specific middleware functions to specific routes e.g.

  • /api can use IP restrictions middleware.
  • /admin can use authentication check middleware.
  • both can use logging and processing time middleware.

Some features of Router:

  • Use express.Router() multiple times to define independent groups of routes.
  • Apply the express.Router() to a section of your site using app.use() e.g. app.use('/api', apiRouter).
  • Use route middleware to process requests.
  • Use route .param() middleware to validate parameters or preform preloading operations.

You can read more on Routing in Express 4.0 on Router documentation.

Application local variables

The app.locals is no longer a function. It is a JavaScript object now. As of 4.x locals merging will not happen automatically as in version 3.x

Version 3.x That operation merges key1 and key2 key-value pairs to app.locals.

    key1: value1,
    key2: value2

Version 4.0

app.locals.key1 = value1;
app.locals.key2 = value2;

Minor changes and improvements

A set of minor changes and improvements has been added like: req.params is now an object instead of an array. There were some issues with req.params being an array before, which you can find on this Stack Overflow question.