If your application tracks user activity and you want to associate events with a visitor, set the tealium_visitor_id attribute in the data object. The value should uniquely identify the current user, either anonymously or with a personal identifier such as an email address.
// A visitor ID could be read from Cookie Header or other function
var myVisitorId = myVisitorIdFunction();
"tealium_visitor_id" : myVisitorId,
"dom.pathname" : "/mypath",
"dom.domain" : "my.example.com",
"dom.title" : "My home page"