app.post('/api/products', (req, res) => {
  let products = [];
  let id = null;
  let cart = JSON.parse(req.body.cart);
  if (!cart) return res.json(products);
  // TODO: replace for loop with .map
  for (var i = 0; i < data.products.length; i++) {
    id = data.products[i].id.toString();
    if (cart.hasOwnProperty(id)) {
      data.products[i].qty = cart[id];
      products.push(data.products[i]);
    }
  }
  return res.json(products);
});

let products = data.products.reduce((result, product) => {
  id = product.id.toString();
  if (cart.hasOwnProperty(id)) {
    product.qty = cart[id];
    result.push(product);
  }
  return result;
}, []);

return res.json(datas.products.map(function(e){

     if(cart[e.id.toString()])
     {
         e.qty = cart[e.id.toString()];
         return e;
     }
     else
     {
         return null;
     }

  }).filter(function(e){
     if(e)
       return true;
     else
       return false;
  });
);