Check if Url is absolute or relative : has base URL or not

isUrlAbsolute

function isUrlAbsolute(url) {
  if (url.indexOf("//") === 0) {
    return true;
  } // URL is protocol-relative (= absolute)
  if (url.indexOf("://") === -1) {
    return false;
  } // URL has no protocol (= relative)
  if (url.indexOf(".") === -1) {
    return false;
  } // URL does not contain a dot, i.e. no TLD (= relative, possibly REST)
  if (url.indexOf("/") === -1) {
    return false;
  } // URL does not contain a single slash (= relative)
  if (url.indexOf(":") > url.indexOf("/")) {
    return false;
  } // The first colon comes after the first slash (= relative)
  if (url.indexOf("://") < url.indexOf(".")) {
    return true;
  } // Protocol is defined before first dot (= absolute)
  return false; // Anything else must be relative
}