You have cloudflare js
http://ajax.cloudflare.com/cdn-cgi/nexp/dok8v=221574e73d/cloudflare.min.js
loaded in your page which posts the message cf-tick
. You can see the file posting a message if you search for the following code in the file :
a.postMessage("cf-tick","*")
If you remove the loading of CloudFlare script, no message will be posted to the webpage.
If you don't want the cf-tick
to get caught in the event listener, you can check if the message is not cf-tick
:
window.addEventListener('message', messageHandler, false);
function messageHandler(event){
if(event.data) {
if(event.data!="cf-tick")
document.getElementById('test').innerHTML = event.data;
}
}