diff --git a/.gitattributes b/.gitattributes
deleted file mode 100644
index 70cce05d2b561714d9fcbcf7785f4638747157fb..0000000000000000000000000000000000000000
--- a/.gitattributes
+++ /dev/null
@@ -1 +0,0 @@
-*.js.es6 gitlab-language=javascript
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 9aecdde266d3d8bed322581c87c35418050bc804..02d0e9f26ff27a7f8d73a0c27e2b233e0c317c76 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -368,7 +368,7 @@ lint:javascript:report:
   stage: post-test
   before_script: []
   script:
-    - find app/ spec/ -name '*.js' -or -name '*.js.es6' -exec sed --in-place 's|/\* eslint-disable .*\*/||' {} \; # run report over all files
+    - find app/ spec/ -name '*.js' -exec sed --in-place 's|/\* eslint-disable .*\*/||' {} \; # run report over all files
     - yarn run eslint-report || true # ignore exit code
   artifacts:
     name: eslint-report
diff --git a/config/karma.config.js b/config/karma.config.js
index a23e62f5022ccb723ad73b035f7feff6e0948585..c1d3751d88ffcb39daab466d552cc3ea2758b941 100644
--- a/config/karma.config.js
+++ b/config/karma.config.js
@@ -36,7 +36,7 @@ module.exports = function(config) {
       { pattern: 'spec/javascripts/fixtures/**/*@(.json|.html|.html.raw)', included: false },
     ],
     preprocessors: {
-      'spec/javascripts/**/*.js?(.es6)': ['webpack', 'sourcemap'],
+      'spec/javascripts/**/*.js': ['webpack', 'sourcemap'],
     },
     reporters: [progressReporter, 'coverage-istanbul'],
     coverageIstanbulReporter: {
diff --git a/config/webpack.config.js b/config/webpack.config.js
index 8e2b11a4145bfccb2ae0cbcd6b30fc895b71145c..cbcc9ac5aeaf42e3e44b40c7d1d4305b64a07049 100644
--- a/config/webpack.config.js
+++ b/config/webpack.config.js
@@ -56,7 +56,7 @@ var config = {
   module: {
     rules: [
       {
-        test: /\.(js|es6)$/,
+        test: /\.js$/,
         exclude: /(node_modules|vendor\/assets)/,
         loader: 'babel-loader',
         options: {
@@ -130,7 +130,7 @@ var config = {
   ],
 
   resolve: {
-    extensions: ['.js', '.es6', '.js.es6'],
+    extensions: ['.js'],
     alias: {
       '~':              path.join(ROOT_PATH, 'app/assets/javascripts'),
       'emojis':         path.join(ROOT_PATH, 'fixtures/emojis'),
diff --git a/doc/development/testing.md b/doc/development/testing.md
index 9b545d7f0f1bf3f0f97d1778fd412624385796ab..5ac7b8dadeb6d406a5ca253c50445cfad2133a76 100644
--- a/doc/development/testing.md
+++ b/doc/development/testing.md
@@ -35,8 +35,8 @@ GitLab uses [Karma] to run its [Jasmine] JavaScript specs. They can be run on
 the command line via `bundle exec karma`.
 
 - JavaScript tests live in `spec/javascripts/`, matching the folder structure of
-  `app/assets/javascripts/`: `app/assets/javascripts/behaviors/autosize.js.es6` has a corresponding
-  `spec/javascripts/behaviors/autosize_spec.js.es6` file.
+  `app/assets/javascripts/`: `app/assets/javascripts/behaviors/autosize.js` has a corresponding
+  `spec/javascripts/behaviors/autosize_spec.js` file.
 - Haml fixtures required for JavaScript tests live in
   `spec/javascripts/fixtures`. They should contain the bare minimum amount of
   markup necessary for the test.
diff --git a/lib/banzai/pipeline/gfm_pipeline.rb b/lib/banzai/pipeline/gfm_pipeline.rb
index b25d6f18d599a0d5ae9feaac6c9f69102a53fcc6..fd4a6a107c2846754c523f3cd9c00fa49790ad0f 100644
--- a/lib/banzai/pipeline/gfm_pipeline.rb
+++ b/lib/banzai/pipeline/gfm_pipeline.rb
@@ -2,10 +2,10 @@ module Banzai
   module Pipeline
     class GfmPipeline < BasePipeline
       # These filters convert GitLab Flavored Markdown (GFM) to HTML.
-      # The handlers defined in app/assets/javascripts/copy_as_gfm.js.es6
+      # The handlers defined in app/assets/javascripts/copy_as_gfm.js
       # consequently convert that same HTML to GFM to be copied to the clipboard.
       # Every filter that generates HTML from GFM should have a handler in
-      # app/assets/javascripts/copy_as_gfm.js.es6, in reverse order.
+      # app/assets/javascripts/copy_as_gfm.js, in reverse order.
       # The GFM-to-HTML-to-GFM cycle is tested in spec/features/copy_as_gfm_spec.rb.
       def self.filters
         @filters ||= FilterArray[
diff --git a/package.json b/package.json
index 9652dd8f9720eaaa5666c569cf0a2f8d8ebcfade..1048e29d0acf45eeb836fe36ae02d81ec6272de2 100644
--- a/package.json
+++ b/package.json
@@ -2,9 +2,9 @@
   "private": true,
   "scripts": {
     "dev-server": "webpack-dev-server --config config/webpack.config.js",
-    "eslint": "eslint --max-warnings 0 --ext .js,.js.es6 .",
-    "eslint-fix": "eslint --max-warnings 0 --ext .js,.js.es6 --fix .",
-    "eslint-report": "eslint --max-warnings 0 --ext .js,.js.es6 --format html --output-file ./eslint-report.html .",
+    "eslint": "eslint --max-warnings 0 --ext .js .",
+    "eslint-fix": "eslint --max-warnings 0 --ext .js --fix .",
+    "eslint-report": "eslint --max-warnings 0 --ext .js --format html --output-file ./eslint-report.html .",
     "karma": "karma start config/karma.config.js --single-run",
     "karma-start": "karma start config/karma.config.js",
     "webpack": "webpack --config config/webpack.config.js",
@@ -62,7 +62,6 @@
     "exclude": [
       "spec/javascripts/test_bundle.js",
       "spec/javascripts/**/*_spec.js",
-      "spec/javascripts/**/*_spec.js.es6",
       "app/assets/javascripts/droplab/**/*"
     ]
   }
diff --git a/spec/features/copy_as_gfm_spec.rb b/spec/features/copy_as_gfm_spec.rb
index ce34f48aaaf59e6142fa3ae1c9be3ca88a0c8fdc..55df7e45f79a0d0f41f939b74be78caa40df530e 100644
--- a/spec/features/copy_as_gfm_spec.rb
+++ b/spec/features/copy_as_gfm_spec.rb
@@ -20,7 +20,7 @@ describe 'Copy as GFM', feature: true, js: true do
     end
 
     # The filters referenced in lib/banzai/pipeline/gfm_pipeline.rb convert GitLab Flavored Markdown (GFM) to HTML.
-    # The handlers defined in app/assets/javascripts/copy_as_gfm.js.es6 consequently convert that same HTML to GFM.
+    # The handlers defined in app/assets/javascripts/copy_as_gfm.js consequently convert that same HTML to GFM.
     # To make sure these filters and handlers are properly aligned, this spec tests the GFM-to-HTML-to-GFM cycle
     # by verifying (`html_to_gfm(gfm_to_html(gfm)) == gfm`) for a number of examples of GFM for every filter, using the `verify` helper.
 
diff --git a/spec/javascripts/test_bundle.js b/spec/javascripts/test_bundle.js
index fae462561e9d29c19d127fb73f95a913b46cdd83..c12b44cea89168f1e8f74fadc18f199f4463337e 100644
--- a/spec/javascripts/test_bundle.js
+++ b/spec/javascripts/test_bundle.js
@@ -48,10 +48,10 @@ describe('Uncovered files', function () {
     './network/branch_graph.js',
   ];
 
-  const sourceFiles = require.context('~', true, /^\.\/(?!application\.js).*\.(js|es6)$/);
+  const sourceFiles = require.context('~', true, /^\.\/(?!application\.js).*\.js$/);
   sourceFiles.keys().forEach(function (path) {
     // ignore if there is a matching spec file
-    if (testsContext.keys().indexOf(`${path.replace(/\.js(\.es6)?$/, '')}_spec`) > -1) {
+    if (testsContext.keys().indexOf(`${path.replace(/\.js$/, '')}_spec`) > -1) {
       return;
     }