Deletes slack public/private channel messages, private chat messages and channel thread replies.

delete-slack-messages.js

#!/usr/bin/env node

// Channel ID is on the the browser URL.: https://mycompany.slack.com/messages/MYCHANNELID/
// Pass it as a parameter: node ./delete-slack-messages.js CHANNEL_ID

// CONFIGURATION #######################################################################################################

const token = 'SLACK TOKEN';
// Legacy tokens are no more supported.
// Please create an app or use an existing Slack App
// Add following scopes in your app from "OAuth & Permissions"
//  - channels:history
//  - groups:history
//  - im:history
//  - mpim:history
//  - chat:write

// VALIDATION ########################################################################################################## 

if (token === 'SLACK TOKEN') {
    console.error('Token seems incorrect. Please open the file with an editor and modify the token variable.');
}

let channel = '';

if (process.argv[0].indexOf('node') !== -1 && process.argv.length > 2) {
    channel = process.argv[2];
} else if (process.argv.length > 1) {
    channel = process.argv[1];
} else {
    console.log('Usage: node ./delete-slack-messages.js CHANNEL_ID');
    process.exit(1);
}

// GLOBALS #############################################################################################################

const https         = require('https')
const baseApiUrl    = 'slack.com';
const historyApiUrl = `/api/conversations.history?channel=${channel}&count=1000&cursor=`;
const deleteApiUrl  = `/api/chat.delete?channel=${channel}&ts=`;
const repliesApiUrl = `/api/conversations.replies?channel=${channel}&ts=`
let   delay         = 300; // Delay between delete operations in milliseconds

// ---------------------------------------------------------------------------------------------------------------------

const sleep = delay => new Promise(r => setTimeout(r, delay));
const get   = url => new Promise((resolve, reject) =>
    https
        .get({hostname: baseApiUrl, path: url, headers: { Authorization: `Bearer ${token}` }}, res => {
            let body = ''

            res.on('data', chunk => (body += chunk))
            res.on('end', () => resolve(JSON.parse(body)))
        })
        .on('error', reject)
);

// ---------------------------------------------------------------------------------------------------------------------

async function deleteMessages(threadTs, messages) {

    if (messages.length == 0) {
        return;
    }

    const message = messages.shift();

    if (message.thread_ts !== threadTs) {
        await fetchAndDeleteMessages(message.thread_ts, ''); // Fetching replies, it will delete main message as well.
    } else {
        const response = await get(deleteApiUrl + message.ts);

        if (response.ok === true) {
            console.log(message.ts + (threadTs ? ' reply' : '') + ' deleted!');
        } else if (response.ok === false) {
            console.log(message.ts + ' could not be deleted! (' + response.error + ')');
    
            if (response.error === 'ratelimited') {
                await sleep(1000);
                delay += 100; // If rate limited error caught then we need to increase delay.
                messages.unshift(message);
            }
        }
    }

    await sleep(delay);
    await deleteMessages(threadTs, messages);
}

// ---------------------------------------------------------------------------------------------------------------------

async function fetchAndDeleteMessages(threadTs, cursor) {

    const response = await get((threadTs ? repliesApiUrl + threadTs + '&cursor=' : historyApiUrl) + cursor);

    if (!response.ok) {
        console.error(response.error);
        return;
    }

    if (!response.messages || response.messages.length === 0) {
        return;
    }

    await deleteMessages(threadTs, response.messages);

    if (response.has_more) {
        await fetchAndDeleteMessages(threadTs, response.response_metadata.next_cursor);
    }
}

// ---------------------------------------------------------------------------------------------------------------------

fetchAndDeleteMessages(null, '');