diff --git a/package.json b/package.json
index d7d852c2fedb4..43d58cabaf944 100644
--- a/package.json
+++ b/package.json
@@ -20,7 +20,7 @@
   },
   "scripts": {
     "lint": "eslint .",
-    "fmt": "prettier --write tools/*.js",
-    "check": "prettier --check tools/*.js"
+    "fmt": "prettier --write tools/*.mjs",
+    "check": "prettier --check tools/*.mjs"
   }
 }
diff --git a/test/test_browser.py b/test/test_browser.py
index 0c7048c7c2eb9..c58099a5df6c0 100644
--- a/test/test_browser.py
+++ b/test/test_browser.py
@@ -2529,7 +2529,7 @@ def test_preload_module(self, args):
     ''')
     self.btest_exit(
       'main.c',
-      args=['-sMAIN_MODULE=2', '--preload-file', '.@/', '-O2', '--use-preload-plugins'] + args)
+      args=['-sMAIN_MODULE=2', '--preload-file', '.@/', '--use-preload-plugins'] + args)
 
   # This does not actually verify anything except that --cpuprofiler and --memoryprofiler compiles.
   # Run interactive.test_cpuprofiler_memoryprofiler for interactive testing.
diff --git a/third_party/mini-lz4.js b/third_party/mini-lz4.js
index 06514fec54de0..f9cbe532e5a0c 100644
--- a/third_party/mini-lz4.js
+++ b/third_party/mini-lz4.js
@@ -343,3 +343,6 @@ return exports;
 
 })();
 
+if (typeof module != 'undefined') {
+  module.exports = MiniLZ4;
+}
diff --git a/tools/file_packager.py b/tools/file_packager.py
index 9f39984b46fca..d4c29ea7d10f1 100755
--- a/tools/file_packager.py
+++ b/tools/file_packager.py
@@ -745,9 +745,8 @@ def generate_js(data_target, data_files, metadata):
       # LZ4FS usage
       temp = data_target + '.orig'
       shutil.move(data_target, temp)
-      meta = shared.run_js_tool(utils.path_from_root('tools/lz4-compress.js'),
-                                [utils.path_from_root('third_party/mini-lz4.js'),
-                                temp, data_target], stdout=PIPE)
+      meta = shared.run_js_tool(utils.path_from_root('tools/lz4-compress.mjs'),
+                                [temp, data_target], stdout=PIPE)
       os.unlink(temp)
       use_data = '''var compressedData = %s;
             compressedData['data'] = byteArray;
diff --git a/tools/lz4-compress.js b/tools/lz4-compress.mjs
similarity index 67%
rename from tools/lz4-compress.js
rename to tools/lz4-compress.mjs
index 1ddd11d3a9b06..bfad03aa03909 100755
--- a/tools/lz4-compress.js
+++ b/tools/lz4-compress.mjs
@@ -4,13 +4,8 @@
 // University of Illinois/NCSA Open Source License.  Both these licenses can be
 // found in the LICENSE file.
 
-'use strict';
-
-const fs = require('fs');
-const path = require('path');
-
-const arguments_ = process.argv.slice(2);
-const debug = false;
+import * as fs from 'fs';
+import * as path from 'path';
 
 function print(x) {
   process.stdout.write(x + '\n');
@@ -20,26 +15,7 @@ function printErr(x) {
   process.stderr.write(x + '\n');
 }
 
-function read(filename, binary) {
-  filename = path.normalize(filename);
-  let ret = fs.readFileSync(filename);
-  if (ret && !binary) ret = ret.toString();
-  return ret;
-}
-
-function readBinary(filename) {
-  return read(filename, true);
-}
-
-function globalEval(x) {
-  eval.call(null, x);
-}
-
-function load(f) {
-  globalEval(read(f));
-}
-
-global.assert = (x, message) => {
+globalThis.assert = (x, message) => {
   if (!x) throw new Error(message);
 };
 
@@ -47,11 +23,16 @@ global.assert = (x, message) => {
 // where we return the decompressed data.
 console.log = printErr;
 
-const lz4 = arguments_[0];
-const input = arguments_[1];
-const output = arguments_[2];
+const MiniLZ4 = await import('../third_party/mini-lz4.js');
 
-load(lz4);
+function readBinary(filename) {
+  filename = path.normalize(filename);
+  return fs.readFileSync(filename);
+}
+
+const arguments_ = process.argv.slice(2);
+const input = arguments_[0];
+const output = arguments_[1];
 
 const data = new Uint8Array(readBinary(input)).buffer;
 const start = Date.now();
diff --git a/tools/preprocessor.mjs b/tools/preprocessor.mjs
index cce73451177de..188f385d97bd5 100755
--- a/tools/preprocessor.mjs
+++ b/tools/preprocessor.mjs
@@ -52,7 +52,7 @@ global.read = (filename) => {
 };
 
 global.load = (f) => {
-  vm.runInThisContext(read(f), { filename: find(f) });
+  vm.runInThisContext(read(f), {filename: find(f)});
 };
 
 assert(args.length >= 2);
@@ -67,6 +67,6 @@ load('parseTools.js');
 
 let output = preprocess(inputFile);
 if (expandMacros) {
-  output = processMacros(output, inputFile)
+  output = processMacros(output, inputFile);
 }
 process.stdout.write(output);