Basic port of Opera's tab traces for Vivaldi

(function tabTraces() {
   const TRACE_LENGTH = 5; // How many tabs to mark as recently visited
   const THICKNESS_PX = 2; // How thick the marker is, in pixels
   const TAB_LIMIT = 15;   // Only mark tabs if there are at least this many in the window

   let recentTabIDs = [];
   let myWindowId = null;

   let styleElement = document.createElement('style');
   document.head.appendChild(styleElement);

   async function generateStyleRulesForRecentTabs() {
      let tabs = await chrome.tabs.query({ windowId: myWindowId });
      if (tabs.length < TAB_LIMIT) {
         styleElement.textContent = "";
         return;
      }

      styleElement.textContent =
         recentTabIDs
            .slice(1, TRACE_LENGTH + 1) //Skip first i.e active tab
            .map((id, i) => {

               let alpha = (0.78 ** i).toFixed(2);

               return `#tab-${id} {
                        border-bottom: ${THICKNESS_PX}px solid rgba(255, 255, 255, ${alpha}) !important;
                        border-radius: var(--currentRadius) var(--currentRadius) ${THICKNESS_PX}px ${THICKNESS_PX}px !important;
                     }`;
            }).join('\n');
   }

   function removeTabFromRecent(tabId) {
      recentTabIDs = recentTabIDs.filter(id => id !== tabId);
   }

   function onActivated({ tabId, windowId }) {
      if (windowId !== myWindowId) return;

      removeTabFromRecent(tabId);
      recentTabIDs.unshift(tabId);

      recentTabIDs = recentTabIDs.slice(0, TRACE_LENGTH + 1); //Removes traces above the limit

      generateStyleRulesForRecentTabs();
   }

   function onRemoved(tabId) {
      removeTabFromRecent(tabId)
      generateStyleRulesForRecentTabs();
   }

   function init() {
      if (!document.getElementById('browser')) {
         return setTimeout(init, 250);
      }

      chrome.windows.getCurrent(win => {
         myWindowId = win.id;
         chrome.tabs.query({ active: true, windowId: myWindowId }, tabs => {
            if (tabs[0]) recentTabIDs.unshift(tabs[0].id);
         });

         chrome.tabs.onActivated.addListener(onActivated);
         chrome.tabs.onRemoved.addListener(onRemoved);
      });
   }

   init();
})();