Answers for "preventdefault stop reloading"

prevent reload javascript

window.onbeforeunload = function() {
  return "Dude, are you sure you want to leave? Think of the kittens!";
}

prevent form from reloading with preventDefault

document.getElementById("defaultsub").addEventListener("click", function(event){
    if(document.querySelector('form').checkValidity()){
     event.preventDefault();
     console.log("Prevent default submission");
     alert("ALERT!!!!!");
}
})