getNewOrRepeat.js

// analytics.page('Name', { returning: getNewOrRepeat() === 'repeat' })

function getNewOrRepeat() {
  var session = 30;   // minutes — feel free to change
  var timeout = 30;   // days — feel free to change
  var cookie = '__nr' // cookie name — feel free to change

  var now = new Date().getTime();
  var day = 24 * 60 * 60 * 1000;
  var minute = 60 * 1000;
  var expires = new Date(new Date().setTime(now + timeout * day)).toUTCString();
  
  var cookieValue = getCookieValue(cookie);

  if (cookieValue) {
    var parts = cookieValue.split('-');
    return now - parts[0] < session * minute && parts[1] == 'new'
      ? saveAndReturn('new')
      : saveAndReturn('repeat');
  }

  return saveAndReturn('new');

  function saveAndReturn(state) {
    document.cookie = cookie +'='+ now +'-'+ state + '; expires=' + expires;
    return state;
  }

  function getCookieValue(cookie) {
    var pairs = document.cookie.split(/ *; */);
    if ('' === pairs[0]) return '';
    for (var i = 0; i < pairs.length; ++i) {
      var parts = pairs[i].split('=');
      if (parts[0] !== cookie) continue;
      return parts[1];
    }
  }
}