Replace method turns out to be faster than the custom function, at least for simple strings and simple regular expressions.

src/randomization.mjs

@@ -1,5 +1,6 @@
 import pkg from "./routes.mjs";
 import { existsSync, readFileSync } from "fs";
+export { paintSource, tryReadFile };
 const {
     cookingInserts,
     vegetables,
@@ -8,53 +9,27 @@ const {
     cacheBustList,
     text404,
   } = pkg;
-export { insertText, paintSource, tryReadFile };
-
-/*
-//  Try this instead of the .replace method. Might be more performant.
-//  Will edit str by replacing all matches of lis with newText.
-//  Usage: insertText(['<Example1>', '<Example2>'],
-//             '<Example1> Big Giant Paragraph <Example2> Smol Paragraph',
-//             stringOrFunctionToGenerateNewText);
-*/
-const insertText = (lis, str, newText) => {
-  let position;
-
-//  The lis argument should be a list of strings containing placeholders.
-//  Ensure lis is formatted as a list, and loop through each of the
-//  placeholder strings.
-  for (let placeholder of [].concat(lis)) {
-//      Find all matches of a placeholder string and insert new text there.
-    while ((position = str.indexOf(placeholder)) != -1)
-      str =
-        str.slice(0, position) +
-        (typeof newText == "function" ? newText() : newText) +
-        str.slice(position + placeholder.length);
-  }
-  return str;
-};
 
 //  Below are lots of function definitions used to obfuscate the website.
 //  This makes the website harder to properly categorize, as its source code
 //  changes with each time it is loaded.
 const randomListItem = (lis) => () => lis[(Math.random() * lis.length) | 0],
-  charset = ["&#173;", "&#8203;", "&shy;", "<wbr>"],
+  charset = /&#173;|&#8203;|&shy;|<wbr>/gi,
   getRandomChar = randomListItem(charRandom),
-  insertCharset = (str) => insertText(charset, str, getRandomChar),
+  insertCharset = (str) => str.replace(charset, getRandomChar),
   getRandomSplash = randomListItem(splashRandom),
-  hutaoInsert = (str) => insertText("<!--HUTAOWOA-->", str, getRandomSplash),
+  hutaoInsert = (str) => str.replaceAll("<!--HUTAOWOA-->", getRandomSplash),
   getCookingText = () =>
     `<span style="display:none" data-fact="${randomListItem(vegetables)()}">${randomListItem(cookingInserts)()}</span>`,
   insertCooking = (str) =>
-    insertText(
+    str.replaceAll(
       "<!-- IMPORTANT-HUTAOCOOKINGINSERT-DONOTDELETE -->",
-      str,
       getCookingText
     ),
 //  This one isn't for obfuscation; it's just for dealing with cache issues.
   cacheBusting = (str) => {
     for (let item of Object.entries(cacheBustList))
-      str = insertText(item[0], str, item[1]);
+      str = str.replaceAll(item[0], item[1]);
     return str;
   },
 //  Apply the final obfuscation changes to an entire file.

src/templates.mjs

@@ -1,4 +1,4 @@
-import { insertText, tryReadFile } from "./randomization.mjs";
+import { tryReadFile } from "./randomization.mjs";
 import path from "path";
 export { loadTemplates as default };
 
@@ -22,17 +22,15 @@ const header = tryReadFile(
   settings = tryReadFile(
     path.normalize(__dirname + "/views/pages/misc/deobf/settings.html")
   ),
-  loadTemplates = (str) => {
-    str = insertText("<!--HEADER-->", str, header);
-    str = insertText("<!--FOOTER-->", str, footer);
+  loadTemplates = (str) =>
+    str.replace("<!--HEADER-->", header)
+        .replace("<!--FOOTER-->", footer)
 
     //  Used only on docs.html
-    str = insertText("<!--DOCS-->", str, documentation);
+        .replace("<!--DOCS-->", documentation)
     //  Used only on faq.html
-    str = insertText("<!--FAQ-->", str, faq);
+        .replace("<!--FAQ-->", faq)
     //  Used only on terms.html
-    str = insertText("<!--TOS-->", str, terms);
-    //  Used only on csel.html
-    str = insertText("<!--SETTINGS-->", str, settings);
-    return str;
-  };
+        .replace("<!--TOS-->", str, terms)
+    //  Used only on header.html
+        .replace("<!--SETTINGS-->", str, settings);