Checks if url is an external url or not.

isexternalurl.js

var isExternalUrl = function (url) {

  /* Tests if valid absolute url, ex:
   * http://www.google.com | https://www.google.com | //www.google.com
   */
  if (new RegExp('^((https?:)?//)', 'i').test(url)) {
    var target = document.createElement('a');
    target.href = url;
    // note: hostname will be empty in IE for local urls
    if (target.hostname.length > 0 &&
      window.location.hostname.toLowerCase() !== target.hostname.toLowerCase()) {
      return true;
    }
  }
  return false;
};