JavaScript to Submit a Form

document.addEventListener("DOMContentLoaded",function(){
    let form = document.getElementById('comment-form');
    form.addEventListener("submit",function(ev){
        ev.preventDefault();
        sendData(form);
    });
});

function sendData(form) {
    const xhr = new XMLHttpRequest();

    // Bind the FormData object and the form element
    const fd = new FormData( form );

    // Define what happens on successful data submission
    xhr.addEventListener( "load", function(ev) {
        console.log(ev.target.responseText);
        form.innerHTML = 'Thank you for your feedback.';
    } );

    // Define what happens in case of error
    xhr.addEventListener( "error", function( ev ) {
        console.log('Oops! Something went wrong.');
    } );

    // Set up our request
    xhr.open( form.getAttribute('method'), form.getAttribute('action') );

    // The data sent is what the user provided in the form
    xhr.send( fd );
}