function isAbsoluteURL(url) {
  // A URL is considered absolute if it begins with "<scheme>://" or "//" (protocol-relative URL).
  // RFC 3986 defines scheme name as a sequence of characters beginning with a letter and followed
  // by any combination of letters, digits, plus, period, or hyphen.
  return /^([a-z][a-z\d+\-.]*:)?\/\//i.test(url);
}
Determines whether the specified URL is absolute

@param {string} url The URL to test

@returns {boolean} True if the specified URL is absolute, otherwise false