diff --git a/ext/bg/js/audio.js b/ext/bg/js/audio.js
index 3efcce46..cd42a158 100644
--- a/ext/bg/js/audio.js
+++ b/ext/bg/js/audio.js
@@ -128,7 +128,7 @@ function audioUrlNormalize(url, baseUrl, basePath) {
         if (url[0] === '/') {
             if (url.length >= 2 && url[1] === '/') {
                 // Begins with "//"
-                url = baseUrl.substr(0, baseUrl.indexOf(':') + 1) + url;
+                url = baseUrl.substring(0, baseUrl.indexOf(':') + 1) + url;
             } else {
                 // Begins with "/"
                 url = baseUrl + url;
diff --git a/ext/bg/js/deinflector.js b/ext/bg/js/deinflector.js
index ce4b2961..e2fb7461 100644
--- a/ext/bg/js/deinflector.js
+++ b/ext/bg/js/deinflector.js
@@ -44,7 +44,7 @@ class Deinflector {
 
                     results.push({
                         source,
-                        term: term.slice(0, -kanaIn.length) + kanaOut,
+                        term: term.substring(0, term.length - kanaIn.length) + kanaOut,
                         rules: rulesOut,
                         definitions: [],
                         reasons: [reason, ...reasons]
diff --git a/ext/bg/js/search.js b/ext/bg/js/search.js
index 56316217..ec5a5972 100644
--- a/ext/bg/js/search.js
+++ b/ext/bg/js/search.js
@@ -207,7 +207,7 @@ class DisplaySearch extends Display {
             const match = /[\*\uff0a]+$/.exec(query);
             if (match !== null) {
                 details.wildcard = true;
-                query = query.substr(0, query.length - match[0].length);
+                query = query.substring(0, query.length - match[0].length);
             }
 
             const valid = (query.length > 0);
diff --git a/ext/bg/js/translator.js b/ext/bg/js/translator.js
index 583d6e31..e27cbdff 100644
--- a/ext/bg/js/translator.js
+++ b/ext/bg/js/translator.js
@@ -327,22 +327,22 @@ class Translator {
         const deinflections = [];
 
         for (let i = text.length; i > 0; --i) {
-            const textSlice = text.slice(0, i);
-            deinflections.push(...this.deinflector.deinflect(textSlice));
+            const textSubstring = text.substring(0, i);
+            deinflections.push(...this.deinflector.deinflect(textSubstring));
         }
 
         return deinflections;
     }
 
-    getDeinflections2(text, text2) {
+    getDeinflections2(text1, text2) {
         const deinflections = [];
 
-        for (let i = text.length; i > 0; --i) {
-            const textSlice = text.slice(0, i);
-            const text2Slice = text2.slice(0, i);
-            deinflections.push(...this.deinflector.deinflect(textSlice));
-            if (textSlice !== text2Slice) {
-                deinflections.push(...this.deinflector.deinflect(text2Slice));
+        for (let i = text1.length; i > 0; --i) {
+            const text1Substring = text1.substring(0, i);
+            const text2Substring = text2.substring(0, i);
+            deinflections.push(...this.deinflector.deinflect(text1Substring));
+            if (text1Substring !== text2Substring) {
+                deinflections.push(...this.deinflector.deinflect(text2Substring));
             }
         }
 
@@ -516,6 +516,6 @@ class Translator {
 
     static getNameBase(name) {
         const pos = name.indexOf(':');
-        return (pos >= 0 ? name.substr(0, pos) : name);
+        return (pos >= 0 ? name.substring(0, pos) : name);
     }
 }
diff --git a/ext/fg/js/popup.js b/ext/fg/js/popup.js
index 1f9317e0..ac96f9e8 100644
--- a/ext/fg/js/popup.js
+++ b/ext/fg/js/popup.js
@@ -391,7 +391,7 @@ class Popup {
     static isOnExtensionPage() {
         try {
             const url = chrome.runtime.getURL('/');
-            return window.location.href.substr(0, url.length) === url;
+            return window.location.href.substring(0, url.length) === url;
         } catch (e) {
             // NOP
         }
diff --git a/ext/mixed/js/audio.js b/ext/mixed/js/audio.js
index ff50dee1..4e9d04fa 100644
--- a/ext/mixed/js/audio.js
+++ b/ext/mixed/js/audio.js
@@ -75,7 +75,7 @@ class TextToSpeechAudio {
         for (const group of m[1].split('&')) {
             const sep = group.indexOf('=');
             if (sep < 0) { continue; }
-            searchParameters[decodeURIComponent(group.substr(0, sep))] = decodeURIComponent(group.substr(sep + 1));
+            searchParameters[decodeURIComponent(group.substring(0, sep))] = decodeURIComponent(group.substring(sep + 1));
         }
 
         if (!searchParameters.text) { return null; }