code: function format() {
    var format = 'es' // default
    var args = process.argv.slice(2)
  
    outer:
    for (var i = 0; i < formats.length; i++) {
      for (var j = 0; j < args.length; j++) {
        if (args[j].slice(0, 2) !== '--') { throw new TypeError('process args usage error'); break outer }
        if (args[j].toLocaleLowerCase().slice(9) === formats[i]) { format = formats[i]; break outer }
      }
    }
    return format
  }
docs: output format type