code: function isImportLoaded(link) {
    return useNative ? link.__loaded ||
        (link.import && link.import.readyState !== 'loading') :
        link.__importParsed;
  }
docs: NOTE: test for native imports loading is based on explicitly watching all imports (see below). However, we cannot rely on this entirely without watching the entire document for import links. For perf reasons, currently only head is watched. Instead, we fallback to checking if the import property is available and the document is not itself loading.