Create a bot to welcome users

The app you'll be creating is a modular Slack app, built using the Slack CLI. Make sure to install the latest version of the Slack CLI before proceeding.

Create a new app with the Slack CLI using the following command:

slack create welcomebot

A new app folder will be created. Shift into that folder in whichever editor you prefer. You'll be bouncing between a few folders so we recommend using one that streamlines switching between files.

Welcome to your Slack app! There may not be a welcoming message, but do not fret, you can make yourself at home here. Slack apps are built around their flexibility; don't be afraid to run wild!

For now though, just make three folders within your app folder. Each folder will contain a fundamental building block of a Slack app:

• functions
• workflows
• triggers

With the setup complete, you can get building!

If you want to follow along without placing the code yourself, you can scaffold your new app using the GitHub repository as a template:

slack create --template https://github.com/slack-samples/deno-welcome-bot

The app manifest provides a sneak peak at what you'll be building throughout the rest of this tutorial. The recipe for the Welcome Bot app calls for:

• two workflows, imported from their files:
  • MessageSetupWorkflow
  • SendWelcomeMessageWorkflow
• one datastore imported from its file:
  • WelcomeMessageDatastore
• and six scopes:
  • chat:write
  • chat:write.public
  • datastore:read
  • datastore:write
  • channels:read
  • triggers:write
  • triggers:read

Put that all together and your manifest.ts file will look like:

import { Manifest } from "deno-slack-sdk/mod.ts";
import { WelcomeMessageDatastore } from "./datastores/messages.ts";
import { MessageSetupWorkflow } from "./workflows/create_welcome_message.ts";
import { SendWelcomeMessageWorkflow } from "./workflows/send_welcome_message.ts";

export default Manifest({
  name: "Welcome Message Bot",
  description:
    "Quick and easy way to setup automated welcome messages for channels in your workspace.",
  icon: "assets/default_new_app_icon.png",
  workflows: [MessageSetupWorkflow, SendWelcomeMessageWorkflow],
  outgoingDomains: [],
  datastores: [WelcomeMessageDatastore],
  botScopes: [
    "chat:write",
    "chat:write.public",
    "datastore:read",
    "datastore:write",
    "channels:read",
    "triggers:write",
    "triggers:read",
  ],
});

We've provided you all this upfront to streamline the tutorial, but you would likely build up your manifest as you add workflows and datastores to your app.

In this step we'll be creating a workflow named MessageSetupWorkflow. This workflow will contain the functions needed for someone in the channel to create a welcome message with a form.

Create a file named create_welcome_message.ts within the workflows folder. There you'll add the following workflow definition:

import { DefineWorkflow, Schema } from "deno-slack-sdk/mod.ts";
import { WelcomeMessageSetupFunction } from "../functions/create_welcome_message.ts";

export const MessageSetupWorkflow = DefineWorkflow({
  callback_id: "message_setup_workflow",
  title: "Create Welcome Message",
  description: " Creates a message to welcome new users into the channel.",
  input_parameters: {
    properties: {
      interactivity: {
        type: Schema.slack.types.interactivity,
      },
      channel: {
        type: Schema.slack.types.channel_id,
      },
    },
    required: ["interactivity"],
  },
});

The input_parameters you need are interactivity and channel. The interactivity parameter enables interactive elements, like the form you'll set up next.

You add functions to workflows by using the addStep method. In this case, you'll be adding the form the user will interact with.

This is done using a built-in function. Built-in functions give you the ability to add common Slack functionality without the need to do so from scratch.

The built-in function to use here is the OpenForm function. Add it to your create_welcome_message.ts workflow like so:

export const SetupWorkflowForm = MessageSetupWorkflow.addStep(
  Schema.slack.functions.OpenForm,
  {
    title: "Welcome Message Form",
    submit_label: "Submit",
    description: ":wave: Create a welcome message for a channel!",
    interactivity: MessageSetupWorkflow.inputs.interactivity,
    fields: {
      required: ["channel", "messageInput"],
      elements: [
        {
          name: "messageInput",
          title: "Your welcome message",
          type: Schema.types.string,
          long: true,
        },
        {
          name: "channel",
          title: "Select a channel to post this message in",
          type: Schema.slack.types.channel_id,
          default: MessageSetupWorkflow.inputs.channel,
        },
      ],
    },
  },
);

This creates a form that will show the following fields:

• "Your welcome message", where the user provides the message as a string of text
• "Select a channel to post this message in", where the user provides the channel for the desired channel.

The user can then submit the form.

When the user submits the form, they'll want confirmation that it is submitted.

You can do this by using the built-in SendEphemeralMessage function. Add the following step to your create_welcome_message.ts workflow:

MessageSetupWorkflow.addStep(Schema.slack.functions.SendEphemeralMessage, {
  channel_id: SetupWorkflowForm.outputs.fields.channel,
  user_id: MessageSetupWorkflow.inputs.interactivity.interactor.id,
  message:
    `Your welcome message for this channel was successfully created! :white_check_mark:`,
});

This function takes the provided message text and sends it to the specified user and channel, both pulled from the OpenForm function step above.

Wonderful! Now let's build functionality to handle that welcome message once its submitted by a user.

The message data needs to be accessible at a later time (when a user joins the channel), so it needs to be stored somewhere, like a datastore.

Within your datastores folder, create a file named messages.ts. Within it, define the datastore:

import { DefineDatastore, Schema } from "deno-slack-sdk/mod.ts";

export const WelcomeMessageDatastore = DefineDatastore({
  name: "messages",
  primary_key: "id",
  attributes: {
    id: {
      type: Schema.types.string,
    },
    channel: {
      type: Schema.slack.types.channel_id,
    },
    message: {
      type: Schema.types.string,
    },
    author: {
      type: Schema.slack.types.user_id,
    },
  },
});

Each attribute is a type of information you want to store. In this case, it's the information from the form submission. Next, you'll fill the datastore with that information.

Within your functions folder, create a file named create_welcome_message.ts. This is where you'll define this custom function.

The custom function you'll add here will take the form input the user provided and store that information in the created datastore.

Add the function definition to the create_welcome_message.ts file:

import { SlackAPIClient } from "deno-slack-api/types.ts";
import { DefineFunction, Schema, SlackFunction } from "deno-slack-sdk/mod.ts";
import { SendWelcomeMessageWorkflow } from "../workflows/send_welcome_message.ts";
import { WelcomeMessageDatastore } from "../datastores/messages.ts";

export const WelcomeMessageSetupFunction = DefineFunction({
  callback_id: "welcome_message_setup_function",
  title: "Welcome Message Setup",
  description: "Takes a welcome message and stores it in the datastore",
  source_file: "functions/create_welcome_message.ts",
  input_parameters: {
    properties: {
      message: {
        type: Schema.types.string,
        description: "The welcome message",
      },
      channel: {
        type: Schema.slack.types.channel_id,
        description: "Channel to post in",
      },
      author: {
        type: Schema.slack.types.user_id,
        description:
          "The user ID of the person who created the welcome message",
      },
    },
    required: ["welcome_message", "channel"],
  },
});

This function provides three properties as input_parameters. These are the three pieces of information you want to pass to the datastore: the welcome message, the channel to post in, and the user ID of the person who created the message.

The actual functionality involves taking those input parameters and putting them into a datastore. Put this right below your function definition within create_welcome_message.ts:

export default SlackFunction(
  WelcomeMessageSetupFunction,
  async ({ inputs, client }) => {
    const uuid = crypto.randomUUID();
    const putResponse = await client.apps.datastore.put<
    typeof WelcomeMessageDatastore.definition
    >({
      datastore: WelcomeMessageDatastore.name,
      item: { id: uuid, channel, message, author },
    });

    if (!putResponse.ok) {
      return { error: `Failed to save welcome message: ${putResponse.error}`};
    }

    // Search for any existing triggers for the welcome workflow
    const triggers = await findUserJoinedChannelTrigger(client, channel);
    if (triggers.error) {
      return { error: `Failed to lookup existing triggers: ${triggers.error}` };
    }

    // Create a new user_joined_channel trigger if none exist
    if (!triggers.exists) {
      const newTrigger = await saveUserJoinedChannelTrigger(client, channel);
      if (!newTrigger.ok) {
        return {
          error: `Failed to create welcome trigger: ${newTrigger.error}`,
        };
      }
    }

    return { outputs: {} };
  },
);

Add the custom function you created as a step in the workflow. This connection allows you to use inputs and outputs from previous steps, which is how you'll get the specific pieces of information.

Pivot back to your create_welcome_message.ts workflow file. Add the following step:

MessageSetupWorkflow.addStep(WelcomeMessageSetupFunction, {
  message: SetupWorkflowForm.outputs.fields.messageInput,
  channel: SetupWorkflowForm.outputs.fields.channel,
  author: MessageSetupWorkflow.inputs.interactivity.interactor.id,
});

export default MessageSetupWorkflow;

Now you've created a workflow that will:

• let a user fill out a form with information for a welcome message
• store the welcome message information in a datastore

You need to create a trigger that will start the workflow, which provides a user the form to fill out.

This app will use a specific type of trigger called a link trigger. Link triggers kick off workflows when a user clicks on their link.

Within your triggers folder, create a file named create_welcome_message_shortcut.ts. Place this trigger definition within that file:

import { Trigger } from "deno-slack-api/types.ts";
import MessageSetupWorkflow from "../workflows/create_welcome_message.ts";

const welcomeMessageTrigger: Trigger<typeof MessageSetupWorkflow.definition> = {
  type: "shortcut",
  name: "Setup a Welcome Message",
  description: "Creates an automated welcome message for a given channel.",
  workflow: `#/workflows/${MessageSetupWorkflow.definition.callback_id}`,
  inputs: {
    interactivity: {
      value: "{{data.interactivity}}",
    },
    channel: {
      value: "{{data.channel_id}}",
    },
  },
};

export default welcomeMessageTrigger;

This defines a trigger that will kick off the provided workflow, message_setup_workflow, along with an added bonus: it'll pass along the channel ID of the channel it was triggered in.

The workflow to send a message to a user needs to be invoked after the message is created in the workflow. It also needs to be invoked whenever a new user joins the channel.

This calls for using a different type of trigger: an event trigger. Event triggers are only invoked when a certain event happens. In this case, our event is user_joined_channel.

Think of your setup function as priming everything needed for that message to send. The final piece to set up is this trigger.

Since it runs at a certain point in a workflow, you'll actually place it within a function file. Within the /functions/create_welcome_message.ts file, locate the TODO that we created earlier and place the trigger definition within the triggers.create method:

const triggerResponse = await client.workflows.triggers.create({
  type: "event",
  name: "Member joined response",
  description: "Triggers when member joined",
  workflow: "#/workflows/send_welcome_message",
  event: {
    event_type: "slack#/events/user_joined_channel",
    channel_ids: [inputs.channel],
  },
  inputs: {
    channel: { value: "{{data.channel_id}}" },
    triggered_user: { value: "{{data.user_id}}" },
  },
});
if (!triggerResponse.ok) {
  const error = `Failed to create a trigger - ${triggerResponse.error}`;
  return { error };
}
return { outputs: {} };

/**
 * findUserJoinedChannelTrigger returns if the user_joined_channel trigger
 * exists for the "Send Welcome Message" workflow in a channel.
 */
export async function findUserJoinedChannelTrigger(
  client: SlackAPIClient,
  channel: string,
): Promise<{ error?: string; exists?: boolean }> {
  // Collect all existing triggers created by the app
  const allTriggers = await client.workflows.triggers.list({ is_owner: true });
  if (!allTriggers.ok) {
    return { error: allTriggers.error };
  }

  // Find user_joined_channel triggers for the "Send Welcome Message"
  // workflow in the specified channel
  const joinedTriggers = allTriggers.triggers.filter((trigger) => (
    trigger.workflow.callback_id ===
      SendWelcomeMessageWorkflow.definition.callback_id &&
    trigger.event_type === "slack#/events/user_joined_channel" &&
    trigger.channel_ids.includes(channel)
  ));

  // Return if any matching triggers were found
  const exists = joinedTriggers.length > 0;
  return { exists };
}

/**
 * saveUserJoinedChannelTrigger creates a new user_joined_channel trigger
 * for the "Send Welcome Message" workflow in a channel.
 */
export async function saveUserJoinedChannelTrigger(
  client: SlackAPIClient,
  channel: string,
): Promise<{ ok: boolean; error?: string }> {
  const triggerResponse = await client.workflows.triggers.create<
    typeof SendWelcomeMessageWorkflow.definition
  >({
    type: "event",
    name: "User joined channel",
    description: "Send a message when a user joins the channel",
    workflow:
      `#/workflows/${SendWelcomeMessageWorkflow.definition.callback_id}`,
    event: {
      event_type: "slack#/events/user_joined_channel",
      channel_ids: [channel],
    },
    inputs: {
      channel: { value: channel },
      triggered_user: { value: "{{data.user_id}}" },
    },
  });

  if (!triggerResponse.ok) {
    return { ok: false, error: triggerResponse.error };
  }
  return { ok: true };
}

This trigger passes the event-related channel and triggered_user values on to your soon-to-be workflow. With those accessible, you can now build out your next workflow.

This second workflow will retrieve the message from the datastore and send it to the channel when a new user joins that channel.

Navigate back to your workflows folder, and create a new file send_welcome_message.ts.

Within that file place the workflow definition:

import { DefineWorkflow, Schema } from "deno-slack-sdk/mod.ts";
import { SendWelcomeMessageFunction } from "../functions/send_welcome_message.ts";

export const SendWelcomeMessageWorkflow = DefineWorkflow({
  callback_id: "send_welcome_message",
  title: "Send Welcome Message",
  description:
    "Posts an ephemeral welcome message when a new user joins a channel.",
  input_parameters: {
    properties: {
      channel: {
        type: Schema.slack.types.channel_id,
      },
      triggered_user: {
        type: Schema.slack.types.user_id,
      },
    },
    required: ["channel", "triggered_user"],
  },
});

This workflow will have two inputs: channel and triggered_user, both acquired from the trigger invocation.

Navigate to the functions folder, and create a new file called send_welcome_message.ts.

Within that file add the definition for a function that uses the inputs channel and triggered_user:

import { DefineFunction, Schema, SlackFunction } from "deno-slack-sdk/mod.ts";
import { WelcomeMessageDatastore } from "../datastores/messages.ts";

export const SendWelcomeMessageFunction = DefineFunction({
  callback_id: "send_welcome_message_function",
  title: "Sending the Welcome Message",
  description: "Pull the welcome messages and sends it to the new user",
  source_file: "functions/send_welcome_message.ts",
  input_parameters: {
    properties: {
      channel: {
        type: Schema.slack.types.channel_id,
        description: "Channel where the event was triggered",
      },
      triggered_user: {
        type: Schema.slack.types.user_id,
        description: "User that triggered the event",
      },
    },
    required: ["channel", "triggered_user"],
  },
});

With the function defined, add the actual functionality right after:

export default SlackFunction(SendWelcomeMessageFunction, async (
  { inputs, client },
) => {
  // Querying datastore for stored messages
  const messages = await client.apps.datastore.query<
    typeof WelcomeMessageDatastore.definition
  >({
    datastore: WelcomeMessageDatastore.name,
    expression: "#channel = :mychannel",
    expression_attributes: { "#channel": "channel" },
    expression_values: { ":mychannel": inputs.channel },
  });

  if (!messages.ok) {
    return { error: `Failed to gather welcome messages: ${messages.error}` };
  }

  // Send the stored messages ephemerally
  for (const item of messages["items"]) {
    const message = await client.chat.postEphemeral({
      channel: item["channel"],
      text: item["message"],
      user: inputs.triggered_user,
    });

    if (!message.ok) {
      return { error: `Failed to send welcome message: ${message.error}` };
    }
  }

  return {
    outputs: {},
  };
});

This creates a function that:

• queries the datastore for stored messages
• posts an ephemeral message using the message item from the datastore with a matching channel channel ID value to the user with the triggered_user user ID.

With the custom function built, add it to your send_welcome_message.ts workflow as a step:

SendWelcomeMessageWorkflow.addStep(SendWelcomeMessageFunction, {
  channel: SendWelcomeMessageWorkflow.inputs.channel,
  triggered_user: SendWelcomeMessageWorkflow.inputs.triggered_user,
});

And with that, you have created the two workflows that contain all the functionality you need to send a custom ephemeral message to a user joining a new channel.

For now, you'll want to locally install the app to the workspace. From the command line, within your app's root folder, run the following command:

slack run

Proceed through the prompts until you have a local server running in that terminal instance.

It's installed! You can't use it quite yet though.

Within a terminal located within that folder, you'll need to create that initial link trigger. You can open a new terminal tab or cancel your running server and restart later if you'd like.

You can do that with the slack trigger create command. Make it so.

slack trigger create --trigger-def triggers/create_welcome_message_shortcut.ts

Since you haven't installed this trigger to a workspace yet, you'll be prompted to install the trigger to a new workspace. Then select an authorized workspace in which to install the app.

When you select your workspace, you will be prompted to choose an app environment for the trigger. Choose the Local option so you can interact with your app while developing locally. The CLI will then finish installing your trigger.

Once your app's trigger is finished being installed, you will see the following output:

📚 App Manifest
   Created app manifest for "welcomebot (local)" in "myworkspace" workspace

⚠️  Outgoing domains
   No allowed outgoing domains are configured
   If your function makes network requests, you will need to allow the outgoing domains
   Learn more about upcoming changes to outgoing domains: https://api.slack.com/future/changelog

🏠 Workspace Install
   Installed "welcomebot (local)" app to "myworkspace" workspace
   Finished in 1.5s

⚡ Trigger created
   Trigger ID:   Ft0123ABC456
   Trigger Type: shortcut
   Trigger Name: Setup a Welcome Message
   Shortcut URL: 
https://slack.com/shortcuts/Ft0123ABC456/XYZ123
...

Copy the URL, paste, and post it in a channel to kick off the first workflow and create a message.

When you're ready to make the app accessible to others, you'll want to deploy it instead of running it:

slack deploy

And then create the trigger again, but choosing the Deployed option this time:

slack trigger create --trigger-def triggers/create_welcome_message_shortcut.ts

Other than that, the steps are the same.

Congratulations! You've successfully built your friendly neighborhood welcome bot, providing a cozy presence to all who enter your desired channel.