feat: migrate from axios to fetch

[WilliamBergamin]

Summary

These changes migrates this project axios to the native Fetch API — a major step toward v8.

What changed

• @slack/web-api — Removed axios, form-data, is-electron, and is-stream. HTTP requests now use globalThis.fetch (or a user-supplied fetch function). The public API surface is simpler: a single fetch option replaces agent, tls, requestInterceptor, and adapter.
• @slack/webhook — Same migration: axios removed, replaced with native fetch.
• @slack/socket-mode — Replaced the ws WebSocket library with undici's spec-compliant WHATWG WebSocket. A new dispatcher option enables proxy and custom TLS configuration. undici is declared as a peer dependency.

Breaking changes

Removed option	Replacement
agent (http/https Agent)	fetch option with a custom dispatcher
tls (pfx, cert, ca, etc.)	fetch option with custom TLS config
requestInterceptor	Wrap the fetch function
adapter	Supply a custom fetch
attachOriginalToWebAPIRequestError	Always attached now
httpAgent (socket-mode)	dispatcher option (undici Dispatcher)

• WebAPIHTTPError.headers type changed from IncomingHttpHeaders to Record<string, string>
• Minimum Node.js version 20

---

Proxy configuration examples

Web API — proxy via custom fetch

const { ProxyAgent, fetch: undiciFetch } = require('undici');
const { WebClient } = require('@slack/web-api');

const dispatcher = new ProxyAgent('http://my-proxy:8080');

const client = new WebClient(process.env.SLACK_BOT_TOKEN, {
  fetch: (url, init) => undiciFetch(url, { ...init, dispatcher }),
});

Socket Mode — proxy via dispatcher

const { SocketModeClient, LogLevel } = require('@slack/socket-mode');
const { ProxyAgent } = require('undici');

const dispatcher = new ProxyAgent('http://my-proxy:8080');

const socketModeClient = new SocketModeClient({
  appToken: process.env.SLACK_APP_TOKEN,
  logLevel: LogLevel.DEBUG,
  // dispatcher is used for BOTH the WebSocket connection
  // AND the HTTP API calls (unless clientOptions.fetch is set)
  dispatcher,
});

Socket Mode — separate proxy for HTTP vs WebSocket

const { SocketModeClient } = require('@slack/socket-mode');
const { ProxyAgent, fetch: undiciFetch } = require('undici');

const wsProxy = new ProxyAgent('http://ws-proxy:8080');
const httpProxy = new ProxyAgent('http://http-proxy:9090');

const socketModeClient = new SocketModeClient({
  appToken: process.env.SLACK_APP_TOKEN,
  // WebSocket connections use this dispatcher
  dispatcher: wsProxy,
  clientOptions: {
    // HTTP API calls use this separate fetch
    fetch: (url, init) => undiciFetch(url, { ...init, dispatcher: httpProxy }),
  },
});

Webhook — proxy via custom fetch

const { IncomingWebhook } = require('@slack/webhook');
const { ProxyAgent, fetch: undiciFetch } = require('undici');

const dispatcher = new ProxyAgent('http://my-proxy:8080');

const webhook = new IncomingWebhook(process.env.SLACK_WEBHOOK_URL, {
  fetch: (url, init) => undiciFetch(url, { ...init, dispatcher }),
});

Custom fetch — override for testing or instrumentation

const { WebClient } = require('@slack/web-api');

const client = new WebClient(process.env.SLACK_BOT_TOKEN, {
  fetch: async (url, init) => {
    console.log(`→ ${init?.method ?? 'GET'} ${url}`);
    const start = Date.now();
    const response = await globalThis.fetch(url, init);
    console.log(`← ${response.status} (${Date.now() - start}ms)`);
    return response;
  },
});

---

Testing

• Unit tests pass for all modified packages (web-api, webhook, socket-mode)
• Integration tests pass (prod-server-integration-tests/)
• End-to-end validation with Bolt.js using this branch: bolt-js#test-bolt-with-sdk-v8
  • Bolt starter template (bolt-js-starter-template) works as expected with these changes
• Proxy configuration, custom fetch override, and advanced transport scenarios validated via dedicated test project: WilliamBergamin/test-slack-node-sdk-8

Requirements

• 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.

[zimeg]

@WilliamBergamin LGTM! This is a fantastic enhancement 🪄 🎩 ✨

I'm leaving a few quibbles and thoughts of small improvements but am so excited for this PR 🏆

• Spacing: I ask for a linebreak after imports
• Documentation: A few inline variables weren't so clear to me at a glance and comments might be nice?
• Slashes: Prefixed methods with "/" might guard against absurd case but brings peace of mind 😉

Let's count this toward #2359 too and I have an open question now about removing the @slack/rtm-api package and might be curious about deprecation as well - seeing the code change is motivating!

[zimeg]

🪬 praise: Solid patterns of the event parameter as a single argument!

[zimeg]

🧠 praise: Ouch! Thanks for adding this note! Am I understanding that messages cross between processes?

[WilliamBergamin]

Yess thanks for pointing this out, I want to see if I can improve this logic slightly but I don't think I can 🤔 currently if you have more then one socket connection then all the ping messages will be received by the pingHandler then it is responsible for filtering relevant ping messages

[zimeg]

🌪️ thought: Fascinating change of what's attached to this websocket!

[zimeg]

💡 praise: Big fan of how this can be reused!

[zimeg]

📚 quibble: A kind request for @jsdoc for what this goes toward might give context to later debugging!

[zimeg]

🌟 praise: Quite a delightful pattern to find with shared unidici defaults!

[zimeg]

📚 question: The expected options and handler values aren't clear to me and I'm wondering if documenting these is still useful alongside the "any" option?

[WilliamBergamin]

Great question maybe adding more @jsdoc make more sense 💯

This is a structural type, its main goal is to prevent our project from directly exposing undici types, this provides users with more flexibility when definingDispatchers and gives use more leeway when the time comes to bump undici version

[srtaalej]

LGTM ⭐ ⭐ ⭐