function emailPage() {
  var messageText = 'I thought you\'d be interested in this article on the NPS website. ' + window.location;
  var subjectText = 'NPS website: '+ document.title;
  var email = prompt("Enter your friend's email address:", '');
    window.location = 'mailto:' + email +
      '?subject=' + encodeURIComponent(subjectText) +
      '&body=' + encodeURIComponent(messageText);
  }