Slack Real Time Messaging API

The @slack/rtm-api package contains a simple, convenient, and configurable client for receiving events and sending simple messages to Slack's Real Time Messaging API. Use it in your app to stay connected to the Slack platform over a persistent Websocket connection.

Note: RTM isn't available for modern scoped apps anymore. We recommend using the Events API and Web API instead. If you need to use RTM (possibly due to corporate firewall limitations), you can do so by creating a legacy scoped app. If you have an existing RTM app, do not update its scopes as it will be updated to a modern scoped app and stop working with RTM.

Installation

$ npm install @slack/rtm-api

Usage

These examples show the most common features of the RTMClient. You'll find even more extensive documentation on the package's website.

Initialize the client

The package exports an RTMClient class. Your app will create an instance of the class for each workspace it communicates with. Creating an instance requires a token from Slack. Apps typically connect to the RTM API using a bot token, which start with xoxb. These tokens are created for apps that have a Bot User, so to connect to the RTM API be sure to add a Bot User in your app configuration page. Once the app is installed to the development workspace, you'll have a bot token.

const { RTMClient } = require('@slack/rtm-api');

// Read a token from the environment variables
const token = process.env.SLACK_BOT_TOKEN;

// Initialize
const rtm = new RTMClient(token);

Connect to Slack

Data from Slack will begin to flow to your program once the client is connected. You'll also be able to send data to Slack after the connection is established. Connecting is as easy as calling the .start() method. This method returns a Promise that resolves to the data returned from the rtm.connect Web API method.

const { RTMClient } = require('@slack/rtm-api');
const token = process.env.SLACK_BOT_TOKEN;

const rtm = new RTMClient(token);

(async () => {
  // Connect to Slack
  const { self, team } = await rtm.start();
})();

It's useful in many apps to keep information about the bot user who you've connected as, as well as the workspace you've connected to. That information has been destructured into the variables self and team above. If you only need the user ID and team ID, you can look those up any time the client is connected as the rtm.activeUserId and rtm.activeTeamId properties. In fact, if you need to know whether the client is connected or not, you can check the rtm.connected property.

Options passed to the .start() method are passed through as arguments to the rtm.connect Web API method. These arguments deal with presence, which is discussed in more detail on the documentation website.

Listen for an event

Apps register functions, called listeners, to be triggered when an event of a specific type is received by the client. If you've used Node's EventEmitter pattern before, then you're already familiar with how this works, since the client is an EventEmitter.

The event argument passed to the listener is an object. It's contents corresponds to the type of event its registered for.

const { RTMClient } = require('@slack/rtm-api');
const token = process.env.SLACK_BOT_TOKEN;
const rtm = new RTMClient(token);

// Attach listeners to events by type. See: https://api.slack.com/events/message
rtm.on('message', (event) => {
  console.log(event);
});

(async () => {
  await rtm.start();
})();

The message event type has a special property called subtype to help organize all the messages inside Slack. The client has a convenient shorthand for listening to events of type message, but filtered to a specific subtype. The shorthand is to add the :: characters, followed by the name of the subtype, to the event type.

const { RTMClient } = require('@slack/rtm-api');
const token = process.env.SLACK_BOT_TOKEN;
const rtm = new RTMClient(token);

// Attach listeners to events by message subtype. See: https://api.slack.com/events/message/channel_purpose
rtm.on('message::channel_purpose', (event) => {
  console.log(event);
});

(async () => {
  await rtm.start();
})();

Send a message

Your app can send simple messages to Slack over the client's connection. In this case, simple means that it cannot send messages that include attachments or blocks, but it can include text, mentions, and links which unfurl. The client has a .sendMessage(text, conversationId) method for sending messages to Slack. That method returns a Promise which resolves once Slack has acknowledged the message with a reply. The resolved value contains information about the sent message, such as the ts identifier. See error handling for details on how your app should deal with a Promise rejection.

const { RTMClient } = require('@slack/rtm-api');
const token = process.env.SLACK_BOT_TOKEN;
const rtm = new RTMClient(token);

// Listen for users who join a channel that the bot user is a member of
// See: https://api.slack.com/events/member_joined_channel
rtm.on('member_joined_channel', async (event) => {
  try {
    // Send a welcome message to the same channel where the new member just joined, and mention the user.
    const reply = await rtm.sendMessage(`Welcome to the channel, <@${event.user}>`, event.channel)
    console.log('Message sent successfully', reply.ts);
  } catch (error) {
    console.log('An error occurred', error);
  }
});

(async () => {
  await rtm.start();
})();

The Web API's chat.postMessage method is capable of sending rich messages more advanced layout and interactions. These rich messages are more attractive and useful for users of your app. Install and import the @slack/web-api package into your app, initialize the WebClient class, and use the .chat.postMessage(options) method to send a rich message. The example above can be rewritten using the following code:

const { RTMClient } = require('@slack/rtm-api');
const token = process.env.SLACK_BOT_TOKEN;
const rtm = new RTMClient(token);

// Import the WebClient, and initialize it with the same bot token
const { WebClient } = require('@slack/web-api');
const web = new WebClient(token);

// Listen for users who join a channel that the bot user is a member of
// See: https://api.slack.com/events/member_joined_channel
rtm.on('member_joined_channel', async (event) => {
  try {
    // Send a welcome message with a button to the same channel where the new member just joined.
    const result = await web.chat.postMessage({
      blocks: [
        {
          type: 'section',
          text: {
            type: 'mrkdwn',
            text: `Welcome to the channel, <@${event.user}>. We're here to help. Let us know if you have an issue.`,
          },
          accessory: {
            type: 'button',
            text: {
              type: 'plain_text',
              text: 'Get Help',
            },
            value: 'get_help',
          },
        },
      ],
      channel: event.channel,
    });
    console.log('Message sent successfully', result.ts);
  } catch (error) {
    console.log('An error occurred', error);
  }
});

(async () => {
  await rtm.start();
})();

Over the RTM API, your bot user can appear to be typing in Slack before it sends a message ("{Bot Display Name} is typing" is shown near the text input). The client has a .sendTyping(conversationId) method to allow your bot to trigger the typing indicator. The method returns a Promise that resolves when Slack has acknowledged the message. The Promise doesn't have a resolved value.

If you decide to use this method, make sure your bot follows up with an actual message. Otherwise, the bot user may appear to be typing for a very long time.

const { RTMClient } = require('@slack/rtm-api');
const token = process.env.SLACK_BOT_TOKEN;
const rtm = new RTMClient(token);

// Listen for users who join a channel that the bot user is a member of
// See: https://api.slack.com/events/member_joined_channel
rtm.on('member_joined_channel', async (event) => {
  try {
    // Send a typing indicator, and wait for 3 seconds
    await rtm.sendTyping(event.channel);
    await (new Promise((resolve) => setTimeout(resolve, 3000)));

    // Send a message (clears typing indicator)
    const reply = await rtm.sendMessage(`Welcome to the channel, <@${event.user}>`, event.channel)
    console.log('Message sent successfully', reply.ts);
  } catch (error) {
    console.log('An error occurred', error);
  }
});

(async () => {
  await rtm.start();
})();

Lifecycle events

The client's connection to Slack has a lifecycle. This means the client can be seen as a state machine which transitions through a few states as it connects, disconnects, reconnects, and synchronizes with Slack. The client emits an event for each state it transitions to throughout its lifecycle. If your app simply needs to know whether the client is connected or not, the .connected boolean property can be checked.

In the table below, the client's states are listed, which are also the names of the events you can use to observe the transition to that state. The table also includes description for the state, and arguments that a listener would receive.

| Event Name | Arguments | Description | |-----------------|-----------------|-------------| | connecting | | The client is in the process of connecting to the platform. | | authenticated | (connectData) - the response from rtm.connect or rtm.start | The client has authenticated with the platform. This is a sub-state of connecting. | | connected | | The client is connected to the platform and incoming events will start being emitted. | | ready | | The client is ready to send outgoing messages. This is a sub-state of connected | | disconnecting | | The client is no longer connected to the platform and cleaning up its resources. It will soon transition to disconnected. | | reconnecting | | The client is no longer connected to the platform and cleaning up its resources. It will soon transition to connecting. | | disconnected | (error) | The client is not connected to the platform. This is a steady state - no attempt to connect is occurring. The error argument will be undefined when the client initiated the disconnect (normal). |

The client also emits events that are part of its lifecycle, but aren't states. Instead, they represent specific moments that might be interesting to your app. The following table lists these events, their description, and includes the arguments that a listener would receive.

| Event Name | Arguments | Description | |-----------------|-----------|-------------| | error | (error) | An error has occurred. See error handling for details. | | slack_event | (eventType, event) | An incoming Slack event has been received. | | unable_to_rtm_start | (error) | A problem occurred while connecting, a reconnect may or may not occur. |

Handle errors

Errors can happen for many reasons: maybe the token isn't valid, maybe you tried to send a message while the client is disconnected, or maybe you just used a bad argument. In these cases, the returned Promise will reject with an Error. You should catch the error and use the information it contains to decide how your app can proceed.

Each error contains a code property, which you can check against the ErrorCode export to understand the kind of error you're dealing with. For example, when Slack responds to your app with an error, that is an ErrorCode.SendMessagePlatformError. These types of errors provide Slack's response body as the data property.

// Import ErrorCode from the package
const { RTMClient, ErrorCode } = require('@slack/rtm-api');
const token = process.env.SLACK_BOT_TOKEN;
const rtm = new RTMClient(token);

rtm.on('member_joined_channel', async (event) => {
  try {
    const reply = await rtm.sendMessage(`Welcome to the channel, <@${event.user}>`, event.channel)
    console.log('Message sent successfully', reply.ts);
  } catch (error) {
    // Check the error code, and when its a platform error, log the whole response
    if (error.code === ErrorCode.SendMessagePlatformError) {
      console.log(error.data);
    } else {
      // Some other error, oh no!
      console.log('Well, that was unexpected.');
    }
  }
});

(async () => {
  await rtm.start();
})();

There are a few more types of errors that you might encounter, each with one of these codes:

• ErrorCode.NoReplyReceivedError: A message was sent, but because either the connection was reset the there was no reply acknowledging it from the server. You may want to send this message again.
• ErrorCode.SendWhileDisconnectedError: You've attempted to send a message while the client was not connected.
• ErrorCode.SendWhileNotReadyError: You've attempted to send a message when the client was authenticated but not ready for outgoing messages.
• ErrorCode.WebsocketError: The Websocket transport underlying the connection has emitted an error.

Logging

The RTMClient will log interesting information to the console by default. You can use the logLevel to decide how much information, or how interesting the information needs to be, in order for it to be output. There are a few possible log levels, which you can find in the LogLevel export. By default, the value is set to LogLevel.INFO. While you're in development, its sometimes helpful to set this to the most verbose: LogLevel.DEBUG.

// Import LogLevel from the package
const { RTMClient, LogLevel } = require('@slack/rtm-api');
const token = process.env.SLACK_BOT_TOKEN;

// Log level is one of the options you can set in the constructor
const rtm = new RTMClient(token, {
  logLevel: LogLevel.DEBUG,
});

(async () => {
  await rtm.start();
})();

All the log levels, in order of most to least information are: DEBUG, INFO, WARN, and ERROR.

You can also choose to have logs sent to a custom logger using the logger option. A custom logger needs to implement specific methods (known as the Logger interface):

| Method | Parameters | Return type | |--------------|-------------------|-------------| | setLevel() | level: LogLevel | void | | setName() | name: string | void | | debug() | ...msgs: any[] | void | | info() | ...msgs: any[] | void | | warn() | ...msgs: any[] | void | | error() | ...msgs: any[] | void |

A very simple custom logger might ignore the name and level, and write all messages to a file.

const { createWriteStream } = require('fs');
const logWritable = createWriteStream('/var/my_log_file'); // Not shown: close this stream

const rtm = new RTMClient(token, {
  // Creating a logger as a literal object. It's more likely that you'd create a class.
  logger: {
    debug(...msgs): { logWritable.write('debug: ' + JSON.stringify(msgs)); },
    info(...msgs): { logWritable.write('info: ' + JSON.stringify(msgs)); },
    warn(...msgs): { logWritable.write('warn: ' + JSON.stringify(msgs)); },
    error(...msgs): { logWritable.write('error: ' + JSON.stringify(msgs)); },
    setLevel(): { },
    setName(): { },
  },
});

(async () => {
  await rtm.start();
})();

More

• User presence subscriptions
• Workspace state snapshot on connection
• Using a custom agent for proxying
• Automatic reconnect
• Custom TLS configuration
• Custom API URL

Requirements

This package supports Node v18 and higher. It's highly recommended to use the latest LTS version of node, and the documentation is written using syntax and features from that version.

Getting Help

If you get stuck, we're here to help. The following are the best ways to get assistance working through your issue:

• Issue Tracker for questions, feature requests, bug reports and general discussion related to these packages. Try searching before you create a new issue.