Add All Users to a Slack Channel

If you've ever tried to create a new default Slack channel within an existing workspace, you know that while it's easy to create a channel that new members are added to automatically, adding existing members to that channel is not so simple. This app solves that problem - installing it into your Slack workspace allows you to add all users currently in the workspace into a given channel with a simple slash command!

How It Works

Your app adds a slash command called /cmd invite-all that triggers the functions/events/slack/command/invite-all.js endpoint in this project. The endpoint first fetches all the existing users in the #general channel 1000 at a time using the members method of the slack.conversations API. It handles pagination for large workspaces as shown below:

let generalChannel = await lib.slack.channels['@0.7.2'].retrieve({
  channel: `#general`
});

let generalChannelMembers = [];
let currentCursor = null;
do {
  let membersResponse = await lib.slack.conversations['@0.2.14'].members({
    channel: generalChannel.id,
    limit: 1000,
    cursor: currentCursor
  });
  currentCursor = membersResponse.response_metadata.next_cursor;
  generalChannelMembers = generalChannelMembers.concat(membersResponse.members);
} while (!!currentCursor);

Next, it fetches all the users in the invoked channel in a similar fashion, then dedupes the users (Slack throws an error when inviting a user who is already in a channel) and invites them in batches with the invite method of the slack.conversations API:

let inviteableMembers = generalChannelMembers.filter((generalChannelMember) => {
  return !newChannelMembers.includes(generalChannelMember);
});

for (let i = 0; i < Math.ceil(inviteableMembers.length / 1000); i++) {
  await lib.slack.conversations['@0.2.14'].invite({
    channel: event.channel_id,
    users: inviteableMembers.slice(i * 1000, (i + 1) * 1000),
    as_user: true
  });
}

It caps it off with an ephemeral message to the command invoker announcing how many members the bot added to the channel.

That's it!

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