ansh · asieduernest12 · Jun 3, 2022 · Jun 1, 2022 · Jun 1, 2022 · Jun 1, 2022
diff --git a/src/ContentScript/index.js b/src/ContentScript/index.js
@@ -1,3 +1,6 @@
+import Logger from '../Logger';
+import NodeObserver from './observer';
+
 const runTimeHandler = typeof browser === 'undefined' ? chrome : browser;
 
 const FIXATION_BREAK_RATIO = 0.33;
@@ -6,7 +9,10 @@ const DEFAULT_SACCADES_INTERVAL = 0;
 const DEFAULT_FIXATION_STRENGTH = 3;
 
 // which tag's content should be ignored from bolded
-const IGNORE_NODE_TAGS = ['STYLE', 'SCRIPT'];
+const IGNORE_NODE_TAGS = ['STYLE', 'SCRIPT', 'BR-SPAN', 'BR-FIXATION', 'BR-BOLD'];
+
+/** @type {NodeObserver} */
+let observer;
 
 // making half of the letters in a word bold
 function highlightText(sentenceText) {
@@ -40,7 +46,7 @@ function makeFixations(/** @type string */ textContent) {
 
 function parseNode(/** @type Element */ node) {
   // some websites add <style>, <script> tags in the <body>, ignore these tags
-  if (IGNORE_NODE_TAGS.includes(node.parentElement.tagName)) {
+  if (!node?.parentElement?.tagName || IGNORE_NODE_TAGS.includes(node.parentElement.tagName)) {
     return;
   }
 
@@ -62,28 +68,50 @@ function parseNode(/** @type Element */ node) {
   if (node.hasChildNodes()) [...node.childNodes].forEach(parseNode);
 }
 
-const ToggleReading = (enableReading) => {
-  console.time('ToggleReading-Time');
-  const boldedElements = document.getElementsByTagName('br-bold');
+function mutationCallback(/** @type MutationRecord[] */ mutationRecords) {
+  Logger.logInfo('mutationCallback fired ', mutationRecords.length);
+  mutationRecords.forEach(({ type, addedNodes }) => {
+    if (type !== 'childList') return;
 
-  if (boldedElements.length < 1) {
-    addStyles();
-    [...document.body.children].forEach(parseNode);
-  }
+    addedNodes?.forEach(parseNode);
+  });
+}
 
-  if (document.body.classList.contains('br-bold') || enableReading === false) {
-    document.body.classList.remove('br-bold');
-    console.timeEnd('ToggleReading-Time');
-    return;
-  }
+const ToggleReading = (enableReading) => {
+  const endTimer = Logger.logTime('ToggleReading-Time');
+  try {
+    const boldedElements = document.getElementsByTagName('br-bold');
 
-  if (!document.body.classList.contains('br-bold')) {
-    document.body.classList.add('br-bold');
-  }
+    if (boldedElements.length < 1) {
+      addStyles();
+    }
 
-  if (enableReading) document.body.classList.add('br-bold');
+    if (document.body.classList.contains('br-bold') || enableReading === false) {
+      document.body.classList.remove('br-bold');
+      observer.destroy();
+      observer = null;
+      return;
+    }
 
-  console.timeEnd('ToggleReading-Time');
+    /**
+   * add .br-bold if it was not present or if enableReading is true
+   * enableReading = true means add .br-bold to document.body when a page loads
+   */
+    if (!document.body.classList.contains('br-bold') || enableReading) {
+      document.body.classList.add('br-bold');
+      [...document.body.children].forEach(parseNode);
+
+      /** make an observer if one does not exist and .br-bold is present on body/active */
+      if (!observer) {
+        observer = new NodeObserver(document.body, null, mutationCallback);
+        observer.observe();
+      }
+    }
+  } catch (error) {
+    Logger.logError(error);
+  } finally {
+    endTimer();
+  }
 };
 
 const onChromeRuntimeMessage = (message, sender, sendResponse) => {

diff --git a/src/ContentScript/observer.js b/src/ContentScript/observer.js
@@ -0,0 +1,29 @@
+export default class NodeObserver {
+  #DEFAULT_MUTATION_OPTIONS = { childList: true, subtree: true };
+
+  /** @type MutationObserver */
+  #observer;
+
+  /** @type MutationCallback */
+  #callback;
+
+  /** @type OberverOptions */
+  #options;
+
+  /** @type Node */
+  #target;
+
+  constructor(target, options, /** @type MutationCallback */ callback) {
+    this.#observer = new MutationObserver(callback);
+    this.#options = options ?? this.#DEFAULT_MUTATION_OPTIONS;
+    this.#target = target;
+  }
+
+  observe() {
+    this.#observer.observe(this.#target, this.#options);
+  }
+
+  destroy() {
+    this.#observer.disconnect();
+  }
+}
diff --git a/src/Logger.js b/src/Logger.js
@@ -0,0 +1,40 @@
+/**
+ *
+ * provide development utility functions for reporting errors, logging data and logging time
+ */
+
+/* eslint-disable no-console */
+export default class Logger {
+  static #isProductionEnv = () => process.env.NODE_ENV === 'production';
+
+  static logError = (error) => {
+    if (this.#isProductionEnv()) return;
+    console.error(error);
+  };
+
+  /**
+ *
+ * @param  {...any} data
+ * @returns {void}
+ */
+  static logInfo = (...data) => {
+    if (this.#isProductionEnv()) return;
+
+    console.log(...data);
+  };
+
+  /**
+ *
+ * @param {String} label
+ * @returns {Function} end and display time when called in non production environment
+ */
+  static logTime = (label) => {
+    if (this.#isProductionEnv()) {
+      return () => {
+      // no-op}
+      };
+    }
+    console.time(label);
+    return () => console.timeEnd(label);
+  };
+}