index.js
function flush(callback) {
    fs.writeFile(_this._filename, JSON.stringify(_this._cache), callback);
  }
function flush(callback) {
    fs.writeFile(_this._filename, JSON.stringify(_this._cache), callback);
  }
function flush ( callback ) { fs . writeFile ( _this . _filename , JSON . stringify ( _this . _cache ) , callback ) ; }
flush cache to disk
flush cache to disk