Discord_MSG_Center.js

// ==UserScript==
// @name         Discord MSG Center
// @version      0.3
// @author       You
// @match        https://discord.com/channels/@me
// @grant        none
// ==/UserScript==

var queryByAttrNameStartsWith = (contextualSelector = '*', prefix = "") => {
  const allSel = document.querySelectorAll(contextualSelector)
  for (let i = 0; i < allSel.length; i++) {
    const classList = allSel[i].classList
    for (let ii = 0; ii < classList.length; ii++) {
      if (classList[ii].startsWith(prefix)) {
        return classList[ii]
      }
    }
  }
  return null
}

function styleWindow() {
  const dd = document.querySelector("div."+queryByAttrNameStartsWith('div', 'recentMentionsPopout-'))
  dd.style.width = "95vw" // 35vw
  dd.style.maxWidth = "90vw" // 600px
  dd.style.maxHeight = "100vh" // 80vh
  dd.style.height = "95vh"
}

;(function() {
    'use strict'
    const delay = 3 // sec

    var button = document.querySelector('[aria-label="Posteingang"]')
    var waitToToggle = false
    var callback = (mutationList, observer) => {
      for (const mutation of mutationList) {
        if (mutation.attributeName === 'aria-expanded') {
          if (mutation.target.getAttribute('aria-expanded') === 'true') { // window is open
            if (waitToToggle) {
              waitToToggle = false
              styleWindow()
            }
          } else if (waitToToggle) { // window is closed
               button.click() // open

          }
        }
      }
    }

    var MsgCheck = () => {
      if (location.href === "https://discord.com/channels/@me") {
        try {
          if (button === null || !button.isConnected) {
            button = document.querySelector('[aria-label="Posteingang"]')
            var observer = new MutationObserver(callback)
            observer.observe(button, { attributes: true })
            window.addEventListener('beforeunload', () => {
              observer.disconnect()
            })
          }

          if (button.getAttribute('aria-expanded') == 'false') { // window is closed
              return
          }

          if (document.querySelectorAll("div[data-list-id]").length > 1) {
            if (document.querySelectorAll("div[data-list-id]")[1].scrollTop !== 0) { // updated only if not scrolled
              return
            }
          }

          waitToToggle = true
          button.click() // close
        } catch(err) {
          console.log(err)
        }
      }
    }

    setInterval(() => {
        MsgCheck()
    }, delay * 1000)
})();