Sending form with AJAX. Source: http://blog.ponyfoo.com/2013/07/09/getting-over-jquery

form.html

<form id='registration' name='registration' action='/register'>
    <input type='text' name='username' value='carlos'>
    <input type='email' name='email' value='[email protected]'>
    <input type='number' name='dob' value='1940'>
    <input type='submit' onclick='return sendForm(this.form);'>
</form>

javascript-only

// Create form data and send it with only JS.
var formData = new FormData();
formData.append('username', 'carlos');
formData.append('email', '[email protected]');
formData.append('dob', 1940);

var xhr = new XMLHttpRequest();
xhr.open('POST', '/register', true);
xhr.onload = function(e){
    if(this.status === 200){
        console.log(this.response);
    }
};
xhr.send(formData);

send-from-form.js

// Take data from the HTML form.
function sendForm(form) {
    var formData = new FormData(form);
    formData.append('csrf', 'e69a18d7db1286040586e6da1950128c');

    var xhr = new XMLHttpRequest();
    xhr.open('POST', form.action, true);
    xhr.onload = function(e) {
        // ...
    };
    xhr.send(formData);

    return false; // we're already submitting the form through AJAX.
}

var form = document.querySelector('#registration');
sendForm(form);