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

Question

I am getting troubles with the post method in fetch because my server is receiving an empty object from the client. I've checked in the client side and can't send the value that I want to send.

This is my server:

const express = require('express');
const app = express();
const bodyParser = require('body-parser');
const mysql = require('mysql');

app.use(bodyParser.json());
app.use(bodyParser.urlencoded({
    extended: true
}));

// connection configurations
const mc = mysql.createConnection({
    host: 'localhost',
    user: 'root',
    password: '12345',
    database: 'node_task_demo',
    //socketPath: '/Applications/MAMP/tmp/mysql/mysql.sock'
});

// connect to database
mc.connect();

// default route
app.get('/', function (req, res) {
    return res.send({ error: true, message: 'hello' })
});

// Here where I'm calling in the client side
app.get('/todos', function (req, res) {
    mc.query('SELECT * FROM tasks', function (error, results, fields) {
        if (error) throw error;
        return res.send({ error: false, data: results, message: 'Todo list' });
    });
});

// Search for todos with ‘bug’ in their name
app.get('/todos/search/:keyword', function (req, res) {
  var mensaje = 'Todos search list.';
    let keyword = req.params.keyword;
    mc.query("SELECT * FROM tasks WHERE task LIKE ? ", ['%' + keyword + '%'], function (error, results, fields) {
        if (error) throw error;
        return res.send({ error: false, data: results, message: mensaje});
    });
});

// Retrieve todo with id
app.get('/todo/:id', function (req, res) {

    let task_id = req.params.id;

    if (!task_id) {
        return res.status(400).send({ error: true, message: 'Please provide task_id' });
    }

    mc.query('SELECT * FROM tasks where id=?', task_id, function (error, results, fields) {
        if (error) throw error;
        return res.send({ error: false, data: results[0], message: 'Todos list.' });
    });

});

// Add a new todo
app.post('/todo/meterla', function (req, res) {

    let task = req.body.task;

    if (!task) {
        return res.status(400).send({ error:true, message: 'Please provide task' });
    }

    //var task = req.body.task;

    var query = mc.query("INSERT INTO tasks SET ? ", { task: task}, function (error, results, fields) {
        if (error) throw error;
        console.log(task);
        return res.send({ error: false, data: results, message: 'New task has been created successfully.' });
    });
});

//  Update todo with id
app.put('/todo', function (req, res) {

    let task_id = req.body.task_id;
    let task = req.body.task;

    if (!task_id || !task) {
        return res.status(400).send({ error: task, message: 'Please provide task and task_id' });
    }

    mc.query("UPDATE tasks SET task = ? WHERE id = ?", [task, task_id], function (error, results, fields) {
        if (error) throw error;
        return res.send({ error: false, data: results, message: 'Task has been updated successfully.' });
    });
});

//  Delete todo
app.delete('/todo', function (req, res) {

    let task_id = req.body.task_id;

    if (!task_id) {
        return res.status(400).send({ error: true, message: 'Please provide task_id' });
    }
    mc.query('DELETE FROM tasks WHERE id = ?', [task_id], function (error, results, fields) {
        if (error) throw error;
        return res.send({ error: false, data: results, message: 'Task has been updated successfully.' });
    });
});

// all other requests redirect to 404
app.all("*", function (req, res, next) {
    return res.send('page not found');
    next();
});

// port must be set to 8080 because incoming http requests are routed from port 80 to port 8080
app.listen(8081, function () {
    console.log('Escuchando por el puerto 8081');
});

// allows "grunt dev" to create a development server with livereload
module.exports = app;

This is my client:

import React, { Component } from 'react';
import logo from './logo.svg';
import './App.css';

class App extends Component {

  constructor(props) {
    super(props);
    this.state = {data: ""};
    this.state_2 = {message: []};
    this.onSubmit = this.handleSubmit.bind(this);
  }

  componentDidMount() {
     fetch('/todo/1')
    .then((response) => response.json())
    .then((responseJson) =>{
      this.setState({
        message: responseJson.data
      });
    })
  }

handleSubmit(e){
  e.preventDefault();
  var self = this;
  // On submit of the form, send a POST request with the data to the server.
  fetch('/todo/meterla',{
    method: 'POST',
    body:{
      task: self.refs.task.value
    }
  })
  .then(function(response){
    return response.json()
  }).then(function(body){
    console.log(body);
    alert(self.refs.task.value)
  });
}

  render() {
    return (
      <div className="App">
        <div className="App-header">
          <img src={logo} className="App-logo" alt="logo" />
          <h2>Welcome to React</h2>
        </div>
        <form onSubmit={this.onSubmit}>
          <input type="text" placeholder="task" ref="task"/>
          <input type="submit"/>
        </form>
        <p className="App-intro">
          Este es el resultado de la consulta = <b>{JSON.stringify(this.state.message)}</b>
        </p>
      </div>
    );
  }
}

export default App;

Answer 1

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)
  });