static void slackReact(S token, S channelID, S timestamp, S emoji) {
  S name = "simple_smile";
  S url = "https://slack.com/api/reactions.add";
  Map postData = litmap("token", token, "channel", channelID, "timestamp", timestamp, "name", emoji);
  print(doPostWithTimeout(postData, url, slackSetTimeout_get()));
}