Useful little snippets for building Slack apps

slack-app-snippets.js

// Username regex
// Starts with @
// Can contain only numbers, lowercase letters, -, ., _
// NOTE: this can be avoided by escaping characters (slash command settings)
const usernameRegex = /^@+[0-9a-z_\-.]*$/;

// Get all user ID mentions from a string
// <@UXXXX|user> (slash commands)
// <@UXXXX> (app mention text)
// Returns an array of user mentions
const getMentions = (text, isSlashcmd = false) => {
  const regex = slashcmd ? /<@U[A-Z0-9]*?\|user>/g : /<@U[A-Z0-9]*?>/g;
  return text.match(regex);
}

/**
 * Message middleware: ignore some kinds of messages
 * A bit hacky to catch inconsistencies in Slack API
 * (Customer service was contacted; unreliable behavior confirmed)
 * @param {object} event event object
 * @return {Promise<void>} continue if not ignored message type
*/
async ignoreMention({ message, event, next }) {
  const disallowedSubtypes = ['channel_topic', 'message_changed'];
  const ignoreSubtypeEvent = disallowedSubtypes.indexOf(event.subtype) > -1;
  const ignoreSubtypeMessage = message && message.subtype && disallowedSubtypes.indexOf(message.subtype) > -1;
  const ignoreEdited = !!event.edited;
  // If mention should be ignored, return
  if (ignoreSubtypeEvent || ignoreSubtypeMessage || ignoreEdited) {
    return;
  }
  // If mention should be processed, continue
  await next();
}