New features in 3.x

Express

• express.application prototype
• express.request prototype
• express.response prototype

Application

• app.head() support
• app.locals object (app.locals.foo = 'bar')
• app.locals(obj) (app.locals({ foo: 'bar', bar: 'baz'}))
• app.render(name[, options], callback) to render app-level views
• app.engine(ext, callback) to map template engines

Settings

• trust proxy setting enables the use of "X-Forwarded-Proto" for req.protocol and res.redirect url construction
• json spaces setting enables the developer to decide if res.json() responds with nicely formatted JSON or compact json (this value is passed to JSON.stringify())
• json replacer setting is a callback which is passed to JSON.stringify() in res.json() allowing you to manipulate and filter the JSON response

Request

• req.path the request pathname
• req.protocol returns the protocol string "http" or "https" (supports X-Forwarded-Proto via trust proxy setting)
• req.get(field) gets a request header field value (req.get('Host'))
• req.accepts(type) improved
• req.accepts(types) added, returns the most viable type
• req.accepted array of parsed Accept values sorted by quality
• req.acceptsCharset(charset) added
• req.acceptedCharsets array of parsed Accept-Charset values sorted by quality
• req.acceptsLanguage(lang) added
• req.acceptedLanguages array of parsed Accept-Language values sorted by quality
• req.signedCookies object containing signed cookies
• req.stale to see if a request is stale (based on ETag/Last-Modified)
• req.fresh to complement req.stale
• req.ips to return an array of X-Forwarded-For values when "trust proxy" is enabled
• req.ip return the upstream addr in req.ips or req.connection.remoteAddress
• req.range(size) parses the Range header field

Response

• res.get(field) gets a response header field value (res.get('Content-Length'))
• res.set(field, value) sets a response header field (res.set('Content-Length', n))
• res.set(obj) set several field values
• res.type(path) alias of previous res.contentType(path), allows res.type('json'), res.type('application/x-whatever')
• res.format(obj) to format responses based on qvalue-sorted Accept
• JSON cookie support (res.cookie('cart', { ids: [1,2,3] }), req.cookies.cart.ids)
• signed cookie support (res.cookie(name, value, { signed: true }))
• res.format(obj) for content-negotiation
• res.locals object (res.locals.foo = 'bar')
• res.locals(obj) (res.locals({ foo: 'bar', bar: 'baz'))
• res.redirect() X-Forwarded-Proto support
• res.redirect() relative support (res.redirect('../new'), res.redirect('./edit'), etc)
• res.links(obj) set the "Link" header field with the given links
• res.jsonp([status], obj) was added for explicit JSONP support