Get all Slack Member IDs of a Channel

getSlackIds.js

// Open up the desired channel in the Slack web interface and run the following to generate display name/id pairs
const channelMembers = members = document.querySelectorAll('#channel_page_all_members div a')

const idNamePairs = {}

members.forEach( (div) => {
  const name = div.children[2].firstElementChild.innerHTML
  idNamePairs[name] = div.getAttribute('data-member-id')
})

console.log(idNamePairs)