Express API version - /v1, /v2, etc..

versionMiddleware.js

const latest = 5;

module.exports = (req, res, next) => {
  if (!req.params.version.match(/^v\d+$/)) { // /v1 or /v2
    return res.sendStatus(404);
  }
  req.version = parseInt(req.params.version.substr(1)); // 1 or 2
  if (!req.version || req.version > latest) {
    return res.sendStatus(404);
  }
  next();
};

versionRouter.js

module.exports = (routeMap) => (req, res, next) => {
  const key = Object.keys(routeMap)
    .filter(version => version <= req.version)
    .pop();
  const route = routeMap[key];
  return route(req, res, next);
};

Usage example:

• index.js

...
app.use('/:version', router)

• router.js

...
const router = express.Router({ mergeParams: true });
const versionRouter = require('./versionRouter')
const versionMiddleware = require('./versionMiddleware');

router.use(versionMiddleware);

router.get('/hello', versionRouter({
  1: (req, res, next) => {
    return res.status(200).json({'message': 'hello 1'})
  },
  2: (req, res, next) => {
    return res.status(200).json({'message': 'hello 2 and 3'})
  },
  4: (req, res, next) => {
    return res.status(200).json({'message': 'hello 4 and higher'})
  }
}));