feat: add support for sayStream listener argument by WilliamBergamin · Pull Request #2841 · slackapi/bolt-js

WilliamBergamin · 2026-03-26T21:10:29Z

Summary

This PR aims to introduce a new listener argument utility sayStream, it enables developers to easily use a WebClient.chatStream object initialized with logical default values.

sayStream is WebClient.chatStream initialized with

channel_id: from the event payload
thread_ts: thread_ts from the event payload or falls back to the ts value if it is available
recipient_team_id: the team_id from the event received or the enterprise_id if the app is installed on the org
recipient_user_id: the user_id from the event received

sayStream is available on app.event and the assistant listeners, if Bolt fails to extract channel_id or thread_ts then sayStream will be undefined

Testing

clone this branch
build the project with npm pack .
Import the package in a Bolt project
Play around with sayStream

Sample app.ts

import { App, LogLevel } from '@slack/bolt';
import 'dotenv/config';

const sleep = (ms: number) => new Promise((r) => setTimeout(r, ms));

const app = new App({
token: process.env.SLACK_BOT_TOKEN,
socketMode: true,
appToken: process.env.SLACK_APP_TOKEN,
logLevel: LogLevel.DEBUG,
});

app.event('app_mention', async ({ sayStream }) => {
const stream = sayStream({ buffer_size: 100 });

await stream.append({ markdown_text: '*Someone rang the bat signal!* :bat:\n\n' });
await sleep(5000);
await stream.append({ markdown_text: "Oh wait, it's just an @mention. Even better!\n\n" });
await stream.append({
  markdown_text: "> Fun fact: I was mass-produced in a mass-production factory, but I like to think I'm *one of a kind*.\n\n",
});
await sleep(1000);
await stream.append({ markdown_text: "Anyway, here's my *totally professional* take:\n\n" });
await stream.append({
  markdown_text: "1. `sayStream` is basically magic — words appear like I'm *actually typing* :sparkles:\n",
});
await sleep(1000);
await stream.append({
  markdown_text: "2. Streaming means you don't have to stare at a blank screen wondering if I ghosted you\n",
});
await sleep(1000);
await stream.append({
  markdown_text: '3. Bolt for JavaScript makes building Slack apps easier than microwaving leftovers\n\n',
});
await sleep(500);
await stream.append({ markdown_text: '_*mic drop*_ :microphone:' });
await stream.stop();
});

app.message('', async ({ sayStream }) => {
const stream = sayStream({ buffer_size: 100 });

await stream.append({ markdown_text: '*Psst...* you just DMed a bot. Bold move. I respect that. :sunglasses:\n\n' });
await sleep(5000);
await stream.append({ markdown_text: 'Let me consult my *vast knowledge database*...\n\n' });
await stream.append({ markdown_text: '```\n[ scanning... ]\n[ found: 1 brain cell ]\n[ deploying it now ]\n```\n\n' });
await sleep(1000);
await stream.append({ markdown_text: 'Okay here\'s the deal:\n\n' });
await sleep(1000);
await stream.append({
  markdown_text: ':rocket: *Streaming responses* means you get to watch me think in real time — terrifying, I know\n',
});
await sleep(1000);
await stream.append({
  markdown_text: ':hammer_and_wrench: *Bolt for JavaScript* is the secret sauce behind my dazzling personality\n',
});
await sleep(1000);
await stream.append({
  markdown_text: ':zap: *Socket Mode* keeps our conversation nice and private — no nosy webhooks here\n\n',
});
await sleep(500);
await stream.append({ markdown_text: "That's all I've got. Don't forget to tip your bot! :robot_face:" });
await stream.stop();
});

(async () => {
try {
  await app.start(process.env.PORT || 3000);
  app.logger.info('Bolt app is running!');
} catch (error) {
  app.logger.error('Unable to start App', error);
}
})();

manifest.json

{
    "_metadata": {
        "major_version": 1,
        "minor_version": 1
    },
    "display_information": {
        "name": "SayStreamTest"
    },
    "features": {
        "app_home": {
            "home_tab_enabled": false,
            "messages_tab_enabled": true,
            "messages_tab_read_only_enabled": false
        },
        "bot_user": {
            "display_name": "SayStreamTest",
            "always_online": false
        }
    },
    "oauth_config": {
        "scopes": {
            "bot": [
                "app_mentions:read",
                "chat:write",
                "im:read",
                "im:write",
                "channels:history",
                "im:history"
            ]
        }
    },
    "settings": {
        "event_subscriptions": {
            "bot_events": [
                "app_mention",
                "message.im"
            ]
        },
        "interactivity": {
            "is_enabled": true
        },
        "org_deploy_enabled": true,
        "socket_mode_enabled": true,
        "token_rotation_enabled": false
    }
}

Requirements (place an `x` in each `[ ]`)

I've read and understood the Contributing Guidelines and have done my best effort to follow them.
I've read and agree to the Code of Conduct.

WilliamBergamin · 2026-03-26T21:13:20Z

src/context/create-say-stream.ts

+export interface SayStreamArguments {
+  buffer_size?: number;
+  channel?: string;
+  thread_ts?: string;
+  recipient_team_id?: string;
+  recipient_user_id?: string;
+}


I made Bolt define its own type but maybe it better is we reused the one from WebClient.chatStream, what do y'all think?

@WilliamBergamin Is it possible to define this as something like:

export interface SayStreamArguments = ArgumentType<WebClient['chatStream']>;

Since I agree it's clear to export this as SayStreamArguments but it'd be nice to find matching @jsdoc perhaps too?

codecov · 2026-03-26T21:14:52Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.58%. Comparing base (0dfaba0) to head (e5ee923).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2841      +/-   ##
==========================================
+ Coverage   93.50%   93.58%   +0.07%     
==========================================
  Files          42       43       +1     
  Lines        7747     7841      +94     
  Branches      678      689      +11     
==========================================
+ Hits         7244     7338      +94     
  Misses        498      498              
  Partials        5        5

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zimeg

@WilliamBergamin Amazing efforts more toward surfacing the latest 🤖 ✨

I'm approving this now with a few thoughts toward exported types and tests but this is good stuff 🚢

zimeg · 2026-03-27T00:45:59Z

src/context/create-say-stream.ts

+export interface SayStreamArguments {
+  buffer_size?: number;
+  channel?: string;
+  thread_ts?: string;
+  recipient_team_id?: string;
+  recipient_user_id?: string;
+}


@WilliamBergamin Is it possible to define this as something like:

export interface SayStreamArguments = ArgumentType<WebClient['chatStream']>;

Since I agree it's clear to export this as SayStreamArguments but it'd be nice to find matching @jsdoc perhaps too?

zimeg · 2026-03-27T00:49:05Z

src/Assistant.ts


+/**
+ * Creates utility `sayStream()` to stream responses in the assistant thread.
+ * https://api.slack.com/methods/chat.stream


Suggested change

* https://api.slack.com/methods/chat.stream

* https://docs.slack.dev/tools/bolt-js/concepts/message-sending#streaming-messages

📚 suggestion: I'm uncertain of the absolute link we use but this might be most current?

zimeg · 2026-03-27T20:46:27Z

test/unit/Assistant.spec.ts

+        assert.exists(assistantArgs.sayStream);
        assert.exists(assistantArgs.setStatus);


🧮 quibble: Here and in a few other places the alphabetics are off. No blocker but might be a quick change?

zimeg · 2026-03-27T20:56:13Z

test/types/say-stream.test-d.ts

🧪 suggestion: It'd be nice to include another listener type here for perhaps expected asserts? I'm not certain what correct behavior is at a glance, but I find the action listeners don't include this argument:

app.action('button_click', async ({ ack, sayStream }) => { await ack(); const stream = sayStream({ buffer_size: 100 }); // ... });

zimeg · 2026-03-27T20:57:00Z

src/helpers.ts

+/**
+ * Extracts ts from the event payload.
+ */
+export function extractEventTs<T extends string>(event: KnownEventFromType<T>): string | undefined {
+  if (hasStringProperty(event, 'ts')) {
+    return event.ts;
+  }
+  return undefined;
+}


🔍 praise: I like the simple implementation to begin! Let's continue to enhance these extractions as edge cases appear I think?

WilliamBergamin added 9 commits March 24, 2026 19:28

end of day commit

b53db2a

Update helpers.spec.ts

85cc474

minor fixes

84a7a53

Merge branch 'main' into say-stream

d6d12a2

improve typing and behavior

e36781d

Add support for sayStream in assistant middleware

c90eed9

Improve based on feedback

b40cdaa

simplify unit test

b334b15

Make it explicit

b594ad5

WilliamBergamin added this to the 4.7.0 milestone Mar 26, 2026

WilliamBergamin requested review from mwbrooks, srtaalej and zimeg March 26, 2026 21:10

WilliamBergamin self-assigned this Mar 26, 2026

WilliamBergamin requested a review from a team as a code owner March 26, 2026 21:10

WilliamBergamin added enhancement M-T: A feature request for new functionality semver:minor javascript Pull requests that update Javascript code labels Mar 26, 2026

Merge branch 'main' into say-stream

9c3c491

WilliamBergamin commented Mar 26, 2026

View reviewed changes

WilliamBergamin added 2 commits March 26, 2026 14:27

Merge branch 'main' into say-stream

de47a36

Merge branch 'main' into say-stream

e5ee923

zimeg changed the title ~~feat: add support for say_stream utility~~ feat: add support for sayStream listener argument Mar 27, 2026

zimeg approved these changes Mar 27, 2026

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feat: add support for sayStream listener argument#2841

feat: add support for sayStream listener argument#2841
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	* https://api.slack.com/methods/chat.stream
	* https://docs.slack.dev/tools/bolt-js/concepts/message-sending#streaming-messages

		assert.exists(assistantArgs.sayStream);
		assert.exists(assistantArgs.setStatus);

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WilliamBergamin commented Mar 26, 2026

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