Using the Fetch HTML5 API to POST a form and get back JSON data.

fetch-response.js

// 3. Use the response
// ================================
responsePromise
	// 3.1 Convert the response into JSON-JS object.
  .then(function(response) {
    return response.json();
  })
  // 3.2 Do something with the JSON data
  .then(function(jsonData) {
  	console.log(jsonData);
    document.getElementById('results').innerText =
    	JSON.stringify(jsonData);
  });

fetch-send.js

// 2. Make the request
// ================================
var url = '/echo/json/';
var fetchOptions = {
  method: 'POST',
  headers,
  body: formData
};

var responsePromise = fetch(url, fetchOptions);

fetch-setup-request.js

// 1. Setup the request
// ================================
// 1.1 Headers
var headers = new Headers();
// Tell the server we want JSON back
headers.set('Accept', 'application/json');

// 1.2 Form Data
// We need to properly format the submitted fields.
// Here we will use the same format the browser submits POST forms.
// You could use a different format, depending on your server, such
// as JSON or XML.
var formData = new FormData();
for (var i = 0; i < formEl.length; ++i) {
  formData.append(formEl[i].name, formEl[i].value);
}

Awesome