diff --git a/config/karma.config.js b/config/karma.config.js
index 3e12575935778764795f41e2abe178864a510d2a..39c9dbe264c2c313ecd0ff75278a8bd8902c3d2f 100644
--- a/config/karma.config.js
+++ b/config/karma.config.js
@@ -5,7 +5,7 @@ const argumentsParser = require('commander');
 const glob = require('glob');
 const webpack = require('webpack');
 const IS_EE = require('./helpers/is_ee_env');
-const webpackConfig = require('./webpack.config.js');
+const webpackConfig = require('./webpack.config');
 
 const ROOT_PATH = path.resolve(__dirname, '..');
 const SPECS_PATH = /^(?:\.[\\/])?(ee[\\/])?spec[\\/]javascripts[\\/]/;
diff --git a/config/webpack.config.js b/config/webpack.config.js
index c2af7197f94bc7dbc2a2e96e32bc8a6af3f255ce..422f60736e76f5a83b269aa85b99862395df02e6 100644
--- a/config/webpack.config.js
+++ b/config/webpack.config.js
@@ -422,7 +422,7 @@ module.exports = {
             );
 
             // eslint-disable-next-line global-require
-            const dllConfig = require('./webpack.vendor.config.js');
+            const dllConfig = require('./webpack.vendor.config');
             const dllCompiler = webpack(dllConfig);
 
             dllCompiler.run((err, stats) => {
diff --git a/scripts/frontend/extract_gettext_all.js b/scripts/frontend/extract_gettext_all.js
index 896790a73bb9a24ff04f706dbe259ba9bec461f1..0a5e2b06971cfd54aeff77af31c647b07fc32fc5 100644
--- a/scripts/frontend/extract_gettext_all.js
+++ b/scripts/frontend/extract_gettext_all.js
@@ -6,7 +6,7 @@ const {
   decorateExtractorWithHelpers,
 } = require('gettext-extractor-vue');
 const vue2TemplateCompiler = require('vue-template-compiler');
-const ensureSingleLine = require('../../app/assets/javascripts/locale/ensure_single_line.js');
+const ensureSingleLine = require('../../app/assets/javascripts/locale/ensure_single_line');
 
 const args = argumentsParser
   .option('-f, --file <file>', 'Extract message from one single file')
diff --git a/scripts/frontend/stylelint/stylelint-utility-classes.js b/scripts/frontend/stylelint/stylelint-utility-classes.js
index 420fe82d826f14b5da43dc01e48dc43ca2e05495..14827145b54b02aa101d7bb594cfd2f07f5d9210 100644
--- a/scripts/frontend/stylelint/stylelint-utility-classes.js
+++ b/scripts/frontend/stylelint/stylelint-utility-classes.js
@@ -1,6 +1,6 @@
 const stylelint = require('stylelint');
 const utils = require('./stylelint-utils');
-const utilityClasses = require('./utility-classes-map.js');
+const utilityClasses = require('./utility-classes-map');
 
 const ruleName = 'stylelint-gitlab/utility-classes';
 
diff --git a/spec/javascripts/lib/utils/mock_data.js b/spec/javascripts/lib/utils/mock_data.js
index c2f79a32377ae93bce834732f1ee227f29f28f0b..f1358986f2ad434788cf97b994028a2aea89812e 100644
--- a/spec/javascripts/lib/utils/mock_data.js
+++ b/spec/javascripts/lib/utils/mock_data.js
@@ -1 +1 @@
-export * from '../../../frontend/lib/utils/mock_data.js';
+export * from '../../../frontend/lib/utils/mock_data';
diff --git a/storybook/config/webpack.config.js b/storybook/config/webpack.config.js
index bdfbc52dad59041e09089d591a9e3b9b504b5f2f..c67f79b55a0b59956377abd9df20929bca641a20 100644
--- a/storybook/config/webpack.config.js
+++ b/storybook/config/webpack.config.js
@@ -5,7 +5,7 @@ const path = require('path');
 const sass = require('node-sass'); // eslint-disable-line import/no-unresolved
 const { buildIncludePaths, resolveGlobUrl } = require('node-sass-magic-importer/dist/toolbox'); // eslint-disable-line import/no-unresolved
 const webpack = require('webpack');
-const gitlabWebpackConfig = require('../../config/webpack.config.js');
+const gitlabWebpackConfig = require('../../config/webpack.config');
 
 const ROOT = path.resolve(__dirname, '../../');
 const TRANSPARENT_1X1_PNG =