Using the native fetch-api to send POST-request encoded like jQuery.ajax does it.

fetch POST like jQuery.js

fetch('/endpoint', {
	method: 'POST',
	headers: new Headers({
		'Content-Type': 'application/x-www-form-urlencoded'
	}),
	body: serialize({
		value: 1,
		nested: {
			value: '2'
		}
	})
})
.then(response => response.json())
.then(data => {
	console.log('Succes', data);
});

function serialize(obj, prefix) {
  var str = [];
  for(var p in obj) {
    if (obj.hasOwnProperty(p)) {
      var k = prefix ? prefix + "[" + p + "]" : p, v = obj[p];
      str.push(typeof v == "object" ?
        serialize(v, k) :
        encodeURIComponent(k) + "=" + encodeURIComponent(v));
    }
  }
  return str.join("&");
}