feat!: migrate from axios to fetch (v8)

[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.

[changeset-bot]

⚠️ No Changeset found

Latest commit: e3bf6ed

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[codecov]

Codecov Report

❌ Patch coverage is 84.00000% with 64 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (v8@edadd31). Learn more about missing BASE report.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@          Coverage Diff          @@
##             v8    #2591   +/-   ##
=====================================
  Coverage      ?   87.20%           
=====================================
  Files         ?       62           
  Lines         ?    10261           
  Branches      ?      417           
=====================================
  Hits          ?     8948           
  Misses        ?     1288           
  Partials      ?       25           

Flag	Coverage Δ
cli-hooks	87.20% <84.00%> (?)
cli-test	87.20% <84.00%> (?)
logger	87.20% <84.00%> (?)
oauth	87.20% <84.00%> (?)
socket-mode	87.20% <84.00%> (?)
web-api	87.20% <84.00%> (?)
webhook	87.20% <84.00%> (?)

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