Dirty node.js script that queries the Slack API to find out who has posted most (or least) into a Slack channel of your choice.

package.json

{
  "name": "channel-stats",
  "version": "1.0.0",
  "description": "Find out who has posted most into a Slack channel",
  "main": "slack.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "Adam Hepton <adam@hepton.org>",
  "license": "ISC",
  "dependencies": {
    "console.table": "^0.8.0",
    "slack-api": "^0.1.12"
  }
}

slack.js

'use strict';

const Slack = require('slack-api').promisify();
require('console.table');

const options = {
  token: "<your valid slack api token>"
};

var messagesByUser = {};

const getChannel = (channelName) => {
  return Slack.channels.list(options).then( (data) => {
    return data.channels.filter( (channel) => {
      return channel.name === channelName;
    }).map( (channel) => {
      return channel.id;
    });
  });
};

const getMessagesInChannel = (channel, latest) => {
  return getMessagesBatch(channel, latest).then(countMessagesPerUserInBatch).then(getNextBatch);
};

const getMessagesBatch = (channel, latest) => {
  console.log('batch requested for ts:', latest || "default");

  options.channel = channel;

  if(latest !== null) {
    options.latest = latest;
  }

  return Slack.channels.history(options).then( (data) => {
    return {
      channel: channel,
      has_more: data.has_more,
      messages: data.messages.filter( (msg) => {
        return msg.hasOwnProperty('user') && !msg.hasOwnProperty('subtype');
      })
    };
  });
};

const getNextBatch = (batch) => {
  if(batch.has_more) {
    let latest = batch.messages.pop().ts;
    return getMessagesInChannel(batch.channel, latest);
  }

  return batch;
};

const countMessagesPerUserInBatch = (batch) => {
  messagesByUser = batch.messages
    .map( (msg) => {
      return msg.user;
    })
    .reduce( (authors, value) => {
      if(authors.hasOwnProperty(value)) {
        authors[value]++;
      } else {
        authors[value] = 1;
      }

      return authors;
    }, messagesByUser);

  return batch;
};

const getActiveUserInformation = () => {
  return Slack.users.list({ token: options.token }).then( (data) => {
    return data.members.filter( (member) => {
        return messagesByUser.hasOwnProperty(member.id) && !member.is_bot;
      })
      .map( (member) => {
      return {
        name: member.real_name,
        username: member.name,
        messages: messagesByUser[member.id]
      }
    });
  });
};

const sortByNumberOfMessages = (authors) => {
  let keys = Object.keys(authors).sort( (a, b) => authors[b].messages - authors[a].messages );
  let sortedAuthors = [];
  keys.forEach( (k) => {
    sortedAuthors.push(authors[k]);
  });

  return sortedAuthors;
};

const displaySummary = (data) => {
  console.table(data);
};

/////////////

getChannel('<the channel to query>')
  .then(getMessagesInChannel)
  .then(getActiveUserInformation)
  .then(sortByNumberOfMessages)
  .then(displaySummary)
  .catch(Slack.errors.SlackError, function (error) {
    console.log('Slack did not like what you did: ' + error.message);
  });

Sample output:

name              username        messages
----------------  --------------  --------
Zack Brown        captainredmuff  1563
das scawp         scawp           1287
Prox o'Moron      prox            1023
Steven Jefferson  stejay          316
Al Paterson       acp85           203
Andy Humphreys    rink            1