diff --git a/packages/rxjs/integration/import/fixtures/commonjs/index.js b/packages/rxjs/integration/import/fixtures/commonjs/index.cjs
similarity index 100%
rename from packages/rxjs/integration/import/fixtures/commonjs/index.js
rename to packages/rxjs/integration/import/fixtures/commonjs/index.cjs
diff --git a/packages/rxjs/integration/import/fixtures/commonjs/package.json b/packages/rxjs/integration/import/fixtures/commonjs/package.json
index 6d0140aaa5..9af4c2e5d5 100644
--- a/packages/rxjs/integration/import/fixtures/commonjs/package.json
+++ b/packages/rxjs/integration/import/fixtures/commonjs/package.json
@@ -2,9 +2,9 @@
   "name": "rxjs-import-test",
   "private": true,
   "version": "0.0.1",
-  "main": "./index.js",
+  "main": "./index.cjs",
   "scripts": {
-    "test": "node ./index.js"
+    "test": "node ./index.cjs"
   },
   "dependencies": {}
 }
diff --git a/packages/rxjs/integration/import/fixtures/webpack-bundle/package.json b/packages/rxjs/integration/import/fixtures/webpack-bundle/package.json
index 547b6e0eaf..8f66e63a6f 100644
--- a/packages/rxjs/integration/import/fixtures/webpack-bundle/package.json
+++ b/packages/rxjs/integration/import/fixtures/webpack-bundle/package.json
@@ -3,7 +3,7 @@
   "private": true,
   "version": "0.0.1",
   "scripts": {
-    "test": "node ./test.js"
+    "test": "node ./test.cjs"
   },
   "dependencies": {
     "html-webpack-plugin": "^5.5.3",
diff --git a/packages/rxjs/integration/import/fixtures/webpack-bundle/test.js b/packages/rxjs/integration/import/fixtures/webpack-bundle/test.cjs
similarity index 97%
rename from packages/rxjs/integration/import/fixtures/webpack-bundle/test.js
rename to packages/rxjs/integration/import/fixtures/webpack-bundle/test.cjs
index 2f2a664bf2..27c05aab05 100644
--- a/packages/rxjs/integration/import/fixtures/webpack-bundle/test.js
+++ b/packages/rxjs/integration/import/fixtures/webpack-bundle/test.cjs
@@ -1,7 +1,7 @@
 const puppeteer = require('puppeteer');
 const Webpack = require('webpack');
 const WebpackDevServer = require('webpack-dev-server');
-const webpackConfig = require('./webpack.config.js');
+const webpackConfig = require('./webpack.config.cjs');
 
 // const __filename = fileURLToPath(import.meta.url);
 // const __dirname = dirname(__filename);
diff --git a/packages/rxjs/integration/import/fixtures/webpack-bundle/webpack.config.js b/packages/rxjs/integration/import/fixtures/webpack-bundle/webpack.config.cjs
similarity index 100%
rename from packages/rxjs/integration/import/fixtures/webpack-bundle/webpack.config.js
rename to packages/rxjs/integration/import/fixtures/webpack-bundle/webpack.config.cjs
diff --git a/packages/rxjs/integration/import/runner.js b/packages/rxjs/integration/import/runner.cjs
similarity index 100%
rename from packages/rxjs/integration/import/runner.js
rename to packages/rxjs/integration/import/runner.cjs
diff --git a/packages/rxjs/package.json b/packages/rxjs/package.json
index 90c26e6051..b4c65ccda0 100644
--- a/packages/rxjs/package.json
+++ b/packages/rxjs/package.json
@@ -61,13 +61,13 @@
   "scripts": {
     "lint": "eslint --ext=ts,js src spec spec-dtslint",
     "dtslint": "npm run lint && tsc -b ./src/tsconfig.types.json",
-    "test": "cross-env TS_NODE_PROJECT=tsconfig.mocha.json mocha --config spec/support/.mocharc.js \"spec/**/*-spec.ts\"",
+    "test": "cross-env TS_NODE_PROJECT=tsconfig.mocha.json mocha --config spec/support/.mocharc.cjs \"spec/**/*-spec.ts\"",
     "test:esm": "node spec/module-test-spec.mjs",
     "test:circular": "dependency-cruiser --validate .dependency-cruiser.json -x \"^node_modules\" dist/esm",
-    "test:import": "node integration/import/runner.js",
+    "test:import": "node integration/import/runner.cjs",
     "compile": "tsc -b ./src/tsconfig.cjs.json ./src/tsconfig.cjs.spec.json ./src/tsconfig.esm.json ./src/tsconfig.types.json ./src/tsconfig.types.spec.json ./spec/tsconfig.json",
     "build:clean": "shx rm -rf ./dist",
-    "build": "yarn build:clean && yarn compile && node ./tools/generate-alias.js",
+    "build": "yarn build:clean && yarn compile && node ./tools/generate-alias.cjs",
     "watch": "nodemon -w \"src/\" -w \"spec/\" -e ts -x npm test",
     "watch:dtslint": "nodemon -w \"src/\" -w \"spec-dtslint/\" -e ts -x yarn dtslint",
     "copy_common_package_files": "node ../../scripts/copy-common-package-files.js"
diff --git a/packages/rxjs/spec/support/.mocharc.js b/packages/rxjs/spec/support/.mocharc.cjs
similarity index 100%
rename from packages/rxjs/spec/support/.mocharc.js
rename to packages/rxjs/spec/support/.mocharc.cjs
diff --git a/packages/rxjs/tools/add-license-to-file.js b/packages/rxjs/tools/add-license-to-file.cjs
similarity index 100%
rename from packages/rxjs/tools/add-license-to-file.js
rename to packages/rxjs/tools/add-license-to-file.cjs
diff --git a/packages/rxjs/tools/generate-alias.js b/packages/rxjs/tools/generate-alias.cjs
similarity index 100%
rename from packages/rxjs/tools/generate-alias.js
rename to packages/rxjs/tools/generate-alias.cjs
diff --git a/packages/rxjs/tools/subject-benchmark.js b/packages/rxjs/tools/subject-benchmark.cjs
similarity index 100%
rename from packages/rxjs/tools/subject-benchmark.js
rename to packages/rxjs/tools/subject-benchmark.cjs