title: NodeJS POST results in undefined
body: <p>All my requests work perfectly except when I try to add an item to an array of json elements, it will return undefined every time.</p>
  
  <p>Controller:</p>
  
  <pre><code>    vm.addOptie = function () {
          var newOptie = {"optie": 'stuur',"prijs": 150};
          $http({
              method: 'post',
              url: 'http://localhost:3000/addGekozenOptie',
              headers: {
                  'Content-Type': 'application/json'
              },
              data: newOptie
          }).then(function (gekozenOpties) {
              vm.gekozenOpties = gekozenOpties.data;
          }).catch(function (err) {
              alert('Er is een fout opgetreden: ' + err);
          })
      }
  </code></pre>
  
  <p>and my router/index.js</p>
  
  <pre><code>var router = require('express').Router();
  var gekozenOpties = require('../public/data/opties.json');
  
  router.post('/addGekozenOptie', function (req, res) {
      var op = req.body;
      gekozenOpties.push(op);
      res.json(gekozenOpties);
  });
  
  module.exports = router;
  </code></pre>
  
  <p>Very frustrating seeing as everything else works fine (get/delete).</p>