code: function indexByBaseFilename(files) {
    return files.reduce(function(result, file) {
      result[getBaseFilename(file)] = file;
      return result;
    }, {});
  }
docs: this function takes a list of fully qualified file paths (including directory, name, fingerprint hash, and extension) and returns them indexed by "base filename", which, in this case means the file path without the fingerprint and extension type. e.g. when given the following array: ``` [ "assets/foo-383483eabdh384.js", "assets/vendor-4392ehad384hd.js" ] ```  `indexByBaseFilename` would return: ``` { "assets/foo": "assets/foo-383483eabdh384.js", "assets/vendor": "assets/vendor-4392ehad384hd.js" } ``` This is used to match sourcemap files to their corresponding js files by ignoring the differing fingerprint hashes and extensions