HTML怎么防止用户复制，毫无意义

body {
  -webkit-user-select: none; /* Safari */
  -moz-user-select: none; /* Firefox */
  -ms-user-select: none; /* IE10+/Edge */
  user-select: none; /* Standard */
}

document.addEventListener('copy', function(e){
  e.preventDefault();
  return false;
});
document.addEventListener('selectstart', function(e){
  e.preventDefault();
  return false;
});