app.js

app.post('/addTodo', (req, res) => {
  const collection = client.db('test').collection('todos')
  var todo = req.body.todo // parse the information from the request's body
  collection.insertOne({title: todo}, function (err, results) {
    if (err) {
      console.log(err)
      res.send('')
      return
    }
    res.send(results.ops[0]) // returns the document we just inserted
  })
})