check if you are connected and you don't have a dead battery.

form-check.js

$('.my-form').submit(function(){
  var battery = window.navigator.battery.level <= 0.05;
  var connectivity = window.navigator.onLine;
  var msg = '';
  if(!battery){
    msg = "you should probably plug in your computer";
  }
  if(!battery && !connectivity){
    msg += ", "
  }
  if(!connectivity){
    msg += " you don't seem to be online";
  }
  if(msg){
    alert("Bugger... " + msg);
    return false;
  }
  return true;
});