code: function get(key) {
    for (var _len = arguments.length, args = Array(_len > 1 ? _len - 1 : 0), _key = 1; _key < _len; _key++) {
      args[_key - 1] = arguments[_key];
    }
  
    var msg = MESSAGES[key];
    if (!msg) throw new ReferenceError("Unknown message " + JSON.stringify(key));
  
    // stringify args
    args = parseArgs(args);
  
    // replace $0 placeholders with args
    return msg.replace(/\$(\d+)/g, function (str, i) {
      return args[--i];
    });
  }
docs: Get a message with $0 placeholders replaced by arguments.