This is a bit of JS that sets a cookie for a popup

Popup JS set cookie

function setCookie(key, value) {
  var expires = new Date();
  expires.setTime(expires.getTime() + (60 * (60 * 1000)) );
  document.cookie = key + '=' + value + ';expires=' + expires.toUTCString() + "; path=/";
}

function getCookie(key) {
  var keyValue = document.cookie.match('(^|;) ?' + key + '=([^;]*)(;|$)');
  return keyValue ? keyValue[2] : null;
}

// set a cookie
if (getCookie('in_development') == 'true') {
  $(".popup-frame").hide();
} else {
  $(".popup-frame").show();
  setCookie('in_development','true');
}

$( ".popup" ).click(function() {
  $(".popup-frame").hide();
});

This is a bit of JS that sets a cookie after seeing the popup and checks to see if there is a cookie set when the person returns