Revert "removes unnecessary theme function"

This reverts commit b59af18.

assets/js/theme.js

@@ -19,7 +19,7 @@ let setThemeSetting = (themeSetting) => {
 
 // Apply the computed dark or light theme to the website.
 let applyTheme = () => {
-  let theme = determineThemeSetting();
+  let theme = determineComputedTheme();
 
   transTheme();
   setHighlight(theme);
@@ -210,6 +210,12 @@ let determineThemeSetting = () => {
   return themeSetting;
 };
 
+// Determine the computed theme, which can be "dark" or "light".
+let determineComputedTheme = () => {
+  let themeSetting = determineThemeSetting();
+  return themeSetting;
+};
+
 let initTheme = () => {
   let themeSetting = determineThemeSetting();