router.js

// The server's main routes function
//
// Supports the following end-points:
// POST /push
// POST /register
// POST /register.php
// GET /health
// GET /health.txt

function router(config, req, res) {
  if (req.url == '/push') {
    if(req.method.toLowerCase() == 'post') {
      pusher(config, req, res);
    } else {
      res.statusCode = 405;
      res.end();
    }
  } else if (req.url == '/register') {
    if(req.method.toLowerCase() == 'post') {
      register(config, req, res);
    } else {
      res.statusCode = 405;
      res.end();
    }
  } else if (req.url == '/register.php') {
    if(req.method.toLowerCase() == 'post') {
      registerLegacy(config, req, res);
    } else {
      res.statusCode = 405;
      res.end();
    }
  } else if (req.url == '/health') {
    if(req.method.toLowerCase() == 'get') {
      info = health(req.connections);
      res.end(JSON.stringify(info));
    } else {
      res.statusCode = 405;
      res.end();
    }
  } else if (req.url == '/health.txt') {
    if(req.method.toLowerCase() == 'get') {
      checkHealth(req, res);
    } else {
      res.statusCode = 405;
      res.end();
    }
  } else {
    res.statusCode = 404;
    res.end();
  };
};


// after extracting 5 functions
// complexity was reduced from 11 to 6

function router(config, req, res) {
  if (req.url == '/push') { 
    pushRoute();
  } else if (req.url == '/register') { 
    registerRoute();
  } else if (req.url == '/register.php') { 
    registerPhpRoute();
  } else if (req.url == '/health') { 
    healthRoute();
  } else if (req.url == '/health.txt') { 
    healthTxtRoute();
  } else {
    res.statusCode = 404;
    res.end();
  }

  function pushRoute() {
    if(req.method.toLowerCase() == 'post') {
      pusher(config,  req, res);
    } else {
      res.statusCode = 405;
      res.end();
    }
  }

  function registerRoute() {
    if(req.method.toLowerCase() == 'post') {
      register(config, req, res);
    } else {
      res.statusCode = 405;
      res.end();
    }
  }

  function registerPhpRoute() {
    if(req.method.toLowerCase() == 'post') {
      registerLegacy(config, req, res);
    } else {
      res.statusCode = 405;
      res.end();
    }
  }

  function healthRoute() {
    if(req.method.toLowerCase() == 'get') {
      info = health(req.connections);
      res.end(JSON.stringify(info));
    } else {
      res.statusCode = 405;
      res.end();
    }
  }

  function healthTxtRoute() {
    if(req.method.toLowerCase() == 'get') {
      checkHealth(req, res);
    } else {
      res.statusCode = 405;
      res.end();
    }
  }
}