ProjectJSnewOrReturningAttribute.js

window["optimizely"].push({
  "type": "addListener",
  "filter": {
    "type": "lifecycle",
    "name": "initialized"
  },
  "handler": function(event) {
    var utils = window.optimizely.get('utils');
    
    utils.waitUntil(function(){
      return typeof(window.optimizely.get('visitor').first_session) == "boolean";
    }).then(function(){
			window.optimizely = window.optimizely || [];
			window.optimizely.push({
  			"type": "user",
  			"attributes": {
   				 "New Visitor": window.optimizely.get('visitor').first_session
 			   }
			});
    });
  }
});