code: function exists(filePath, cb) {
    fs.access(filePath, function (err) {
      var exists;
      if (err && err.code === 'ENOENT') {
        exists = false;
        err = null;
      } else if (!err) {
        exists = true;
      }
      cb(err, exists);
    });
  }
docs: /* istanbul ignore next 
  Asynchronously test whether a file exists or not by using `fs.access` modified from https://github.com/nodejs/io.js/issues/1592#issuecomment-98392899.
  
  @function exists
  @param {String} filePath Input file path
  @param {Function} callback Has signature `(err, exists)`
  
  @example
  var exists = io.exists('path/to/data.tsv', function (err, exists) {
  console.log(exists) // `true` if the file exists, `false` if not.
  })