"Injection works OK for text change."

public/injection.js

@@ -1,3 +1,7 @@
+import {DEBUG as debug} from '../src/common.js';
+
+const DEBUG = debug || true;
+
 export function getInjection({sessionId}) {
   // Notes:
     // say() function
@@ -8,7 +12,19 @@ export function getInjection({sessionId}) {
       // in future
   return `
     {
-      if ( top === self ) {
+      const DEBUG = ${DEBUG};
+      const MIN_CHECK_TEXT = 3000;  // min time between checking documentElement.innerText
+      const MIN_NOTIFY = 5000;      // min time between telling controller text maybe changed
+      const MAX_NOTIFICATIONS = 13; // max times we will tell controller text maybe changed
+      const OBSERVER_OPTS = {
+        subtree: true,
+        childList: true,
+        characterData: true
+      };
+      const Top = globalThis.top;
+      let lastInnerText;
+
+      if ( Top === globalThis ) {
         const ConsoleInfo = console.info.bind(console);
         const JSONStringify = JSON.stringify.bind(JSON);
         const TITLE_CHANGES = 10;
@@ -16,6 +32,8 @@ export function getInjection({sessionId}) {
         const TIME_MULTIPLIER = Math.E;
         const sessionId = "${sessionId}";
         const sleep = ms => new Promise(res => setTimeout(res, ms));
+        const handler = throttle(handleFrameMessage, MIN_NOTIFY);
+        let count = 0;
 
         installTop();
 
@@ -25,7 +43,7 @@ export function getInjection({sessionId}) {
           say({install: { sessionId, startUrl }});
           await sleep(500);
           beginTitleChecks();
-          beginTextChecks();
+          beginTextNotifications();
           console.log("Installed.");
         }
 
@@ -61,29 +79,72 @@ export function getInjection({sessionId}) {
           ConsoleInfo(JSONStringify(thing));
         }
 
-        function beginTextChecks() {
+        function beginTextNotifications() {
           // listen for {textChanged:true} messages
           // throttle them
           // on leading throttle edge send message to controller with 
           // console.info(JSON.stringify({textChanged:true}));
-          self.addEventListener('message', ({data, origin}) => {
-            try {
-              
-            } catch(e) {
+          self.addEventListener('message', messageParser);
 
+          console.log('Begun notifying of text changes.');
+
+          function messageParser({data, origin}) {
+            let source;
+            try {
+              ({source} = data.frameTextChangedNotification);
+              if ( count > MAX_NOTIFICATIONS ) {
+                self.removeEventListener('message', messageParser);
+                return;
+              }
+              count++;
+              handler({textChanged:{source}});
+            } catch(e) {
+              DEBUG && console.warn('could not parse message', data, e);
             }
-          });
+          }
+        }
+
+        function handleFrameMessage({textChanged}) {
+          const {source} = textChanged;
+          console.log('Telling controller that text changed');
+          say({textChanged:true, source, count});
         }
       } 
 
-      function beginDocumentMutationChecks() {
+      beginTextMutationChecks();
+
+      function beginTextMutationChecks() {
         // create mutation observer for text
         // throttle output
-        // on leading throttle edge send top.postMessage({textChanged:true}, '*');
+
+        const observer = new MutationObserver(check, /*throttle(check, MIN_CHECK_TEXT)*/);
+        observer.observe(document.documentElement || document, OBSERVER_OPTS);
+
+        console.log('Begun observing text changes.');
+        
+        function check() {
+          console.log('check');
+          const textMutated = document.documentElement.innerText !== lastInnerText;
+          if ( textMutated ) {
+            DEBUG && console.log('Text changed');
+            lastInnerText = document.documentElement.innerText;
+            Top.postMessage({frameTextChangedNotification:{source:location.href}}, '*');
+          }
+        }
       }
 
       // javascript throttle function
-
+		  // source: https://stackoverflow.com/a/59378445	
+			function throttle(func, timeFrame) {
+				var lastTime = 0;
+				return function (...args) {
+					var now = new Date();
+					if (now - lastTime >= timeFrame) {
+						func.apply(this, args);
+						lastTime = now;
+					}
+				};
+			}
     }
   `;
 }