works with popup

content.js

 chrome.runtime.onMessage.addListener(function (msg, sender, sendResponse) {
+  console.log('!! chrome.runtime.onMessage.addListener !!');
+  console.log('ID -- 0002');
+  console.log('msg.text: ' + msg.text);
+  console.log(msg);
 
-  if (msg.text === 'get_all_usernames') {
+  if (msg.text == 'get_all_usernames') {
     sendResponse(findRedditUsernames());
   }
 
-});
+  if (msg.text == 'mark_members') {
+    console.log('!! mark_members !!');
+    if (msg.userlist) {
+      console.log('msg.userlist.length == ' + msg.userlist.length);
+    } else {
+      console.log('msg.userlist not defined');
+    }
 
+    markMemberUsers(msg.userlist);
+    sendResponse(true);
+  }
+
+});
 
 function findRedditUsernames() {
-  var d = document.all[0];
+  var all = document.all[0].querySelectorAll('div.content[role="main"] p.tagline a.author');
+  var li = [];
 
-  if (domContent) {
-    //domContent = domContent.replace('\n', ' ');
-    //domContent = domContent.replace('\r', ' ');
-    var matches = [];
+  for (var i=0; i<all.length; i++)
+    li.push(all[i].innerHTML);
 
-    // Use DOM transverse to find usernames -----
-    var all = document(domContent).querySelectorAll('.author');
+  return li;
+}
 
-    for (var i=0; i<all.length; i++) {
-      matches.push(all[i].href);
-    }
+function markMemberUsers(userlist) {
+  var s = userlist.join('<br>');
+  var elHead = document.getElementsByTagName('head')[0];
+  var elContent = document.all[0].querySelector('div.content[role="main"]');
+  var ico = 'icon.png'
 
-    // Use Regex to find usernames -----
-    // g -> global match
-    // m -> multiline
-    /*
-    var re = new RegExp('(?:\<a href\=\"https?\://www\.reddit\.com/user/)([a-zA-Z0-9_-]+)(?:/?\" )', 'gm');
-    var match = null;
-    while (match = re.exec(domContent)) {
-      if ( matches.indexOf(match[1]) < 0 )
-        matches.push(match[1]);
-    } */
-
-    if (matches) {
-      renderStatus('Regex raw username matches: ' + matches.length);
-      return matches;
-    } else {
-      renderStatus('Regex did not find any username matches.');
-    }
-  }
+  elHead.innerHTML += '<style>.reddmeet-icon { display: block; overflow: hidden; width: 1em; height: 1em; background: transparent url(chrome-extension://__MSG_@@extension_id__/icon12.png) center center no-repeat; background-size: cover; border: 0; margin: 0; padding: 0; }</style>';
 
-  return [];
-}
\ No newline at end of file
+  elContent.innerHTML = '';
+  for (var i=0; i<=userlist.length; i++) {
+    elContent.innerHTML += '<p><span class="reddmeet-icon"></span> ' + userlist[i] + '</p';
+  }
+}

popup.js

@@ -5,20 +5,32 @@ Object.prototype.getName = function() {
    return (results && results.length > 1) ? results[1] : "";
 };
 
+// http://stackoverflow.com/a/13486540/5520354
+function unique_set(arr) {
+  return arr.filter(function (e, i, arr) {
+    return arr.lastIndexOf(e) === i;
+  });
+}
+
 
 ///////////////////////////////////////////////////////////////////////
 
+var currCount = 0;
+var currTab = null;
+var currUsers = null;
 
 document.addEventListener('DOMContentLoaded', function() {
-  renderStatus('Loading...');
-
   getCurrentTabUrl(function(tab) {
     if ( isRedditUrl(tab.url) ) {
-      renderStatus('This is Reddit...');
-      chrome.tabs.sendMessage(tab.id, {text: 'get_all_usernames'}, receiveUsernamesList);
-    }
-    else {
-      renderStatus('Some other website.');
+      currTab = tab;
+
+      if (currUsers === null) {
+        currCount += 1; renderStatus('['+currCount+']');
+        currUsers = []; // This prevents the userlist to be generated again.
+        chrome.tabs.sendMessage(currTab.id, {text: 'get_all_usernames'}, receiveUserlist);
+      }
+
+      renderStatus('Loading...');
     };
   });
 });
@@ -28,35 +40,28 @@ document.addEventListener('DOMContentLoaded', function() {
 
 
 function isRedditUrl(url) {
-    var re = new RegExp("^https?://(\w+\.)+reddit.com(:\d+)?[$/]");
-    return url.match(re);
+  var re = new RegExp("^https?://(\w+\.)+reddit.com(:\d+)?[$/]");
+  return url.match(re);
 }
 
 function getCurrentTabUrl(callback) {
   var queryInfo = { active: true, currentWindow: true, };
+
   chrome.tabs.query(queryInfo, function(tabs) {
     var tab = tabs[0];
     callback(tab);
   });
 }
 
-
-
-function receiveUsernamesList(usernamesList) {
-  // receives document.all[0] object from content.js
-  // domContent = domContent ? domContent : '';
-  renderStatus('DOM content with ' + domContent.length + ' chars... ');
-  var text = 'Still loading...';
-
-  if (domContent) {
-    var foundUser = findRedditUsernames(domContent);
-    rmUsers = queryReddmeetUsernames(foundUser);
-    text = 'FOUND: ';
-    for (var i=0; i<rmUsers.length && i<100; i++)
-      text += rmUsers[i] + ', ';
+function receiveUserlist(userlist) {
+  if (!userlist) {
+    renderStatus('Did NOT get userlist :( ');
+    return;
   }
-
-  renderStatus(text);
+  currUsers = queryReddmeetUsernames(unique_set(userlist));
+  chrome.tabs.sendMessage(currTab.id, {text: 'mark_members', 'userlist': userlist}, function(response){
+    //renderStatus(' !returned from mark_member_usernames! ');
+  });
 }
 
 function renderStatus(statusText) {
@@ -69,6 +74,3 @@ function queryReddmeetUsernames(users) {
   // ::: TODO :::
   return users;
 }
-
-
-/* chrome.browserAction.onClicked.addListener(function (tab) { }); */