Post an object with fetch using react js and express API server

body must be stringified + don't forget the content-type

 fetch('/todo/meterla',{
    method: 'POST',
    body: JSON.stringify({
      task: self.refs.task.value
    }),
    headers: {"Content-Type": "application/json"}
  })
  .then(function(response){
    return response.json()
  }).then(function(body){
    console.log(body);
    alert(self.refs.task.value)
  });