var url = 'https://example.com/profile';

var data = {username: 'example'};

fetch(url, {

  method: 'POST', // or 'PUT'

  body: JSON.stringify(data), // data can be `string` or {object}!

  headers: new Headers({

    'Content-Type': 'application/json'

  })

}).then(res => res.json())

.catch(error => console.error('Error:', error))

.then(response => console.log('Success:', response));

var formData = new FormData();

var fileField = document.querySelector("input[type='file']");

formData.append('username', 'abc123');

formData.append('avatar', fileField.files[0]);

fetch('https://example.com/profile/avatar', {

  method: 'PUT',

  body: formData

})

.then(response => response.json())

.catch(error => console.error('Error:', error))

.then(response => console.log('Success:', response));

var formData = new FormData();

var photos = document.querySelector("input[type='file'][multiple]");

formData.append('title', 'My Vegas Vacation');

formData.append('photos', photos.files);

fetch('https://example.com/posts', {

  method: 'POST',

  body: formData

})

.then(response => response.json())

.then(response => console.log('Success:', JSON.stringify(response)))

.catch(error => console.error('Error:', error));