text: let button = document.getElementById("button");
  button.disabled = true;
  
  let username = document.getElementById("username");
  let passwd = document.getElementById('password');
  let confirm = document.getElementById('confirm-password');
  
  function check() {
      if( username.value && passwd.value && confirm.value==passwd.value )
  	button.disabled = false;
      else
  	button.disabled = true;
  };
  username.onchange = check;
  passwd.onchange = check;
  confirm.onchange = check;
  