Reload a page when modified on the server

live-refresh.js

var origModified = "";
var check = function(){ 
  var xhr = new XMLHttpRequest();
  xhr.open("HEAD", window.location.href, true);
  xhr.onreadystatechange = function() {
    if (this.readyState != 2) return;
    var lastModified = xhr.getResponseHeader("Last-Modified");
    if (!origModified) origModified = lastModified;
    else if (origModified != lastModified) location.reload(true);
  };
  xhr.send();
};
setInterval(check, 120000);
check();