measureSlackMessageResponseTime.js

const send = function(content) {
  const waitFor = (condFunc, cb, timeout = 5) => new Promise((resolve) => {
    const f = () => {
      if (condFunc()) {
        resolve()
      } else {
        setTimeout(f, timeout)
      }
    }
    setTimeout(f, timeout)
  })
  const getLastMessageId = () => [...document.querySelectorAll(".c-virtual_list__item")].slice(-1)[0].id
  document.querySelector(".ql-editor > p").textContent = content
  const lastOtherPersonMessageId = getLastMessageId()
  setTimeout(async () => {
    document.querySelector("button.c-wysiwyg_container__button--send").click()
    console.time("Slack message")
    let lastMessageId
    await waitFor(() => {
      lastMessageId = getLastMessageId()
      return !lastMessageId.includes("x") && lastMessageId !== lastOtherPersonMessageId
    })
    await waitFor(() => getLastMessageId() !== lastMessageId)
    console.timeEnd("Slack message")
  }, 100)
}