Merge branch 'eslint' into 'master'

Add ESLint

## What does this MR do?

- create `package.json`
- add ESLint dependencies to `package.json`
- add JavaScript linting to CI
- add Rake task `lint:javascript`as alias for `eslint` (which itself is an alias for `npm run eslint`)

## Are there points in the code the reviewer needs to double check?

Probably not.

## Why was this MR needed?

My hovercraft was full of eels.

## What are the relevant issue numbers?

- https://gitlab.com/gitlab-org/gitlab-ce/issues/13224#note_12537431
- https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5006#note_13255658


See merge request !5445

2 files changed, 16 insertions, 0 deletions

diff --git a/lib/tasks/eslint.rake b/lib/tasks/eslint.rake
new file mode 100644
index 00000000000..d43cbad1909
--- /dev/null
+++ b/lib/tasks/eslint.rake
@@ -0,0 +1,7 @@
+unless Rails.env.production?
+  desc "GitLab | Run ESLint"
+  task :eslint do
+    system("npm", "run", "eslint")
+  end
+end
+
diff --git a/lib/tasks/lint.rake b/lib/tasks/lint.rake
new file mode 100644
index 00000000000..32b668df3bf
--- /dev/null
+++ b/lib/tasks/lint.rake
@@ -0,0 +1,9 @@
+unless Rails.env.production?
+  namespace :lint do
+    desc "GitLab | lint | Lint JavaScript files using ESLint"
+    task :javascript do
+      Rake::Task['eslint'].invoke
+    end
+  end
+end
+