fetch('https://httpbin.org/post', {
  method: 'POST',
  headers: {
    'Accept': 'application/json, text/plain, */*',
    'Content-Type': 'application/json'
  },
  body: JSON.stringify({a: 7, str: 'Some string: &=&'})
}).then(res => res.json())
  .then(res => console.log(res));