diff --git a/src/newsreader/js/lib/theme.js b/src/newsreader/js/lib/theme.js
index ee7ef48..7d89c5f 100644
--- a/src/newsreader/js/lib/theme.js
+++ b/src/newsreader/js/lib/theme.js
@@ -1,8 +1,8 @@
-function isCSSVariablesSupported() {
+const isCSSVariablesSupported = () => {
   return window.CSS && window.CSS.supports('color', 'var(--fake-color');
-}
+};
 
-function changeTheme(e) {
+const changeTheme = event => {
   const currentPref = sessionStorage.getItem('t-dark');
   const isDark = currentPref && currentPref === 'true' ? true : false;
 
@@ -14,12 +14,12 @@ function changeTheme(e) {
 
   try {
     sessionStorage.setItem('t-dark', !isDark);
-  } catch (e) {
+  } catch (error) {
     // do nothing.
   }
-}
+};
 
-function prefersDarkTheme() {
+const getThemePreference = () => {
   try {
     const currentPref = sessionStorage.getItem('t-dark');
 
@@ -33,12 +33,12 @@ function prefersDarkTheme() {
     } else {
       return false;
     }
-  } catch (e) {
+  } catch (error) {
     return false;
   }
-}
+};
 
-function toggleDarkTheme(isDark) {
+const toggleDarkTheme = isDark => {
   if (isDark) {
     document.documentElement.classList.add('dark-theme');
   } else {
@@ -47,30 +47,30 @@ function toggleDarkTheme(isDark) {
 
   try {
     sessionStorage.setItem('t-dark', isDark);
-  } catch (e) {
+  } catch (error) {
     // do nothing.
   }
-}
+};
 
-function initThemeSelector() {
+const initThemeSelector = () => {
   const themeButton = document.getElementsByClassName('theme-switcher')[0];
-  const mqPrefersDarkTheme = window.matchMedia('(prefers-color-scheme: dark)');
+  const prefersDarkTheme = window.matchMedia('(prefers-color-scheme: dark)');
 
-  if (prefersDarkTheme()) {
+  if (getThemePreference()) {
     toggleDarkTheme(true);
   }
 
   themeButton.addEventListener('click', changeTheme);
 
-  mqPrefersDarkTheme.addListener(mq => {
-    toggleDarkTheme(mq.matches);
+  prefersDarkTheme.addListener(mediaQuery => {
+    toggleDarkTheme(mediaQuery.matches);
   });
-}
+};
 
-function init() {
+const init = () => {
   if (isCSSVariablesSupported()) {
     initThemeSelector();
   }
-}
+};
 
 init();