slack-reactions.js

const process = require('process')
const https = require('https')

const slackToken = process.env.SLACK_TOKEN
if (!process.env.SLACK_TOKEN) {
  console.error('Environment variable SLACK_TOKEN is empty!')
  process.exit(1)
}
if (!process.argv[2]) {
  console.error('usage: node slack-reactions.js MESSAGE_URL')
  process.exit(2)
}

function get(url) {
  let body = ''
  return new Promise((resolve, reject) => {
    https.get(url, (res) => {
      res.on('data', (chunk) => {
        body += chunk
      })
      res.on('end', () => {
        resolve({data: JSON.parse(body)})
      })
    })
  })
}

function parseMessageUrl(url) {
  // message url example:
  // https://your-workspace-name.slack.com/archives/C1234567890/p1536906698000100
  let m = url.match(/.*archives\/(\w+)\/p(\d+)/)
  return {
    channel: m[1],
    messageTs: Number(m[2]) / 1000000
  }
}

async function run() {
  let { channel, messageTs } = parseMessageUrl(process.argv[2])
  const messageTsPlus = messageTs + 1

  try {
    const history = await get(`https://slack.com/api/channels.history?token=${slackToken}&latest=${messageTsPlus}&oldest=${messageTs}&channel=${channel}`)
    history.data.messages[0].reactions.forEach(reaction => {
      reaction.users.forEach(async (userKey) => {
        const user = await get(`https://slack.com/api/users.info?token=${slackToken}&user=${userKey}`)
        console.log(user.data.user.profile.real_name)
      })
    })
  } catch (e) {
  }
}

run()