GASlacker

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A lightweight Slack Web API client for Google Apps Script.

• 168 Slack Web API methods organized like the official SDKs: slack.chat.postMessage({...}) — full parity with Slack's official SDK method list (minus admin.* and discontinued APIs)
• Bearer authorization + JSON requests, with automatic retry on rate limits (HTTP 429, honoring Retry-After)
• File uploads implemented with the current 3-step external upload flow (files.uploadV2)
• OAuth v2 (oauth.v2.access) and modern APIs such as canvases.* / assistant.threads.*
• Zero runtime dependencies — a single bundle.js for the GAS V8 runtime
• Cursor pagination helper: slack.paginate('conversations.list', { limit: 200 }, 'get')
• Escape hatch for any method: slack.call('some.method', params)

Every endpoint name in this library is verified to exist on the live Slack API (dead endpoints answer unknown_method; see tests/routing.spec.ts), and a weekly CI job checks parity against Slack's official SDK method list — when Slack ships new APIs, an issue is filed automatically.

Installation

No build step is required — dist/bundle.js in this repository is the ready-to-use distributable. Choose one:

A. Add the published library (easiest)

1. In your Apps Script project, open Libraries and add this script ID:

   101aZZYpRRnr5AGkVIo8t_yo4kHb7xryLfq3w-HVPpQ4fX0Tkxv3UJyzc
   

2. Pick the latest version, keep the identifier GASlacker, and call GASlacker.methods(token).

To pin your own copy instead, create a standalone Apps Script project, paste dist/bundle.js into it, and deploy it as your own library.

B. Paste directly into your project

Copy dist/bundle.js into your Apps Script project as a script file and call methods(token) directly (no GASlacker. prefix).

C. Push with clasp

Clone this repository, copy the local clasp configuration template, and replace YOUR_SCRIPT_ID with your own Apps Script project ID:

cp .clasp.example.json .clasp.json
pnpm install
pnpm run deploy   # build + clasp push

To rebuild dist/bundle.js yourself, run pnpm install && pnpm run build (Node.js 22.12+ and pnpm required).

Quick start

Save your bot token in Script Properties as SLACK_ACCESS_TOKEN, then:

var token = PropertiesService.getScriptProperties().getProperty('SLACK_ACCESS_TOKEN')
var slack = GASlacker.methods(token)

function hello() {
  var res = slack.chat.postMessage({ channel: 'C0123456789', text: 'Hello World' })
  if (!res.ok) {
    Logger.log(res.error)
  }
}

Every method returns a response object — check ok / error yourself. Slack JSON responses are preserved; an exhausted HTTP 429 is normalized as described under rate-limit retries below.

Receiving Slack events safely

Do not process Slack Events API requests directly in an Apps Script doPost Web App. Slack requires the raw request body plus the X-Slack-Signature and X-Slack-Request-Timestamp headers for request verification, but Apps Script does not expose incoming request headers to doPost(e). A public handler that acts on the JSON body alone can be forged by anyone who learns its URL.

Receive and verify events in an HTTP service that exposes request headers (for example, Cloud Run or Cloud Functions), acknowledge them within three seconds, and keep GASlacker for outbound Web API calls from trusted Apps Script workflows. See Slack's request verification and Events API documentation.

Calling any method

slack.call('chat.postMessage', { channel: 'C0123456789', text: 'Hi' })
slack.call('conversations.list', { limit: 20 }, 'get')

// Token rotation is form-encoded and must not carry an Authorization header
var tokenFree = GASlacker.methods(null)
tokenFree.call('tooling.tokens.rotate', { refresh_token: refreshToken }, 'form')

Pagination

paginate follows response_metadata.next_cursor and returns one response per page (with the same rate-limit retries as every other call):

var pages = slack.paginate('conversations.list', { limit: 200 }, 'get')
var channels = pages.flatMap(function (p) {
  return p.channels || []
})

Uploading files

files.uploadV2 wraps Slack's 3-step upload flow (files.getUploadURLExternal → upload → files.completeUploadExternal) in one call:

var blob = Utilities.newBlob('hello', 'text/plain', 'hello.txt')
slack.files.uploadV2({ channel_id: 'C0123456789', file: blob, initial_comment: 'A file!' })

// or upload a string as a file
slack.files.uploadV2({ channel_id: 'C0123456789', content: 'hello', filename: 'hello.txt' })

Pass a GAS Blob as file, or a string as content (with filename). The individual steps are also exposed (slack.files.getUploadURLExternal / slack.files.completeUploadExternal) if you need finer control.

OAuth v2

slack.oauth.access({
  client_id: clientId,
  client_secret: clientSecret,
  code: code,
  redirect_uri: redirectUri,
})

oauth.access, openid.connect.token, and tooling.tokens.rotate are sent without an Authorization header because their exchange credentials are in the request body and Slack rejects an unrelated bearer token. openid.connect.userInfo is the opposite — it needs the user token the exchange returned, so build a client with it: GASlacker.methods(userToken).openid.connect.userInfo().

TypeScript

Type definitions are generated into dist/types/. In a clasp + TypeScript project, copy that folder in and include it in your tsconfig.json — gas-global.d.ts declares the GASlacker global (library use) and the methods global (direct paste), so all 168 methods autocomplete.

Rate-limit retries

GASlacker.methods(token, retriesLimit) — retriesLimit is the number of extra attempts on HTTP 429 (default 3; integer from 0 to 10; 0 sends exactly one request). Waits for the Retry-After header between attempts. If every attempt is rate-limited, the method returns { ok: false, error: 'ratelimited', retry_after: seconds } without sleeping after the final response. Retry waits are capped at five minutes in total, so a longer single wait or repeated long waits return that structured response instead of exhausting Apps Script's execution time.

Examples

Copy-paste-ready scripts live in examples/:

• notify-from-spreadsheet.js — daily sheet summary with Block Kit
• upload-and-paginate.js — file upload + walking all channels

API coverage

Property	Slack API family
slack.api	api.test, plus call() / paginate() for arbitrary methods
slack.apps	apps.* (incl. connections, event.authorizations, manifest, user)
slack.assistant	assistant.threads.*
slack.auth	auth.* (incl. teams.list)
slack.bookmarks	bookmarks.*
slack.bots	bots.*
slack.calls	calls.* (incl. participants)
slack.canvases	canvases.* (incl. access / sections)
slack.chat	chat.* (incl. startStream / appendStream / stopStream)
slack.conversations	conversations.* (incl. canvases, Slack Connect invites)
slack.dialog	dialog.* (legacy)
slack.dnd	dnd.*
slack.emoji	emoji.*
slack.entity	entity.presentDetails
slack.files	files.* (incl. remote, 3-step upload)
slack.functions	functions.*
slack.oauth	oauth.v2.access
slack.openid	openid.connect.* (Sign in with Slack)
slack.pins	pins.*
slack.reactions	reactions.*
slack.reminders	reminders.*
slack.search	search.*
slack.slackLists	slackLists.* (Lists API)
slack.stars	stars.* (superseded by "Later" but still served)
slack.team	team.* (incl. profile, billing, preferences, externalTeams)
slack.tooling	tooling.tokens.rotate
slack.usergroups	usergroups.* (incl. users)
slack.users	users.* (incl. profile, setPhoto, discoverableContacts)
slack.views	views.*
slack.workflows	workflows.featured.*

Method names mirror Slack's exactly — including delete: chat.delete(), files.delete(), canvases.delete(). (The older delete_ aliases still work.)

Removed / not included

• Legacy channels.* / groups.* / im.* / mpim.* / rtm.*
• files.comments.* and apps.permissions.* (discontinued by Slack; they answer unknown_method)
• files.upload (v1, discontinued) — use files.uploadV2
• admin.* enterprise methods (out of scope; use slack.call() if needed)

Development

pnpm run lint        # oxlint
pnpm run typecheck   # tsc --noEmit
pnpm run test        # vitest
pnpm run build       # lint + typecheck + test + vite build
pnpm run deploy      # build + clasp push

See docs/verification.md for the manual verification plan against the real Slack API, and CONTRIBUTING.md for how to add a new API method.

Reference

• Slack Web API docs: https://docs.slack.dev/reference/methods/
• Inspired by os/slacker and soundTricker/SlackApp

License

MIT License. See LICENSE.txt.