lnreader-plugins/libs/isAbsoluteUrl.js

const isUrlAbsolute = (url) => {
    if (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
  };
  
module.exports = isUrlAbsolute;