slack.js

import fetch from 'node-fetch';

const channel = 'C03T4C7MS';
const channelInfoUrl = `https://slack.com/api/channels.info?token=${token}&channel=${channel}`;
const userListUrl = `https://slack.com/api/users.list?token=${token}`;

async function fetchUsers() {
  try {
    let usersInChannel = await fetch(channelInfoUrl).then(res => res.json());
    usersInChannel = usersInChannel.channel.members;
    const allUsers = await fetch(userListUrl).then(res => res.json());
    const result = usersInChannel.map(userId => {
      const user = allUsers.members.find(user => user.id === userId);
      return {
        name: user.real_name,
        id: user.id,
        image: user.profile.image_512
      }
    })
    return result;
  } catch (e) {
    console.log('e', e);
  }
}

fetchUsers().then(users => console.log(users));