eslint_d

eslint_d

Makes eslint the fastest linter on the planet.

"But eslint is pretty fast already, right?"

Yes, it's actually super fast. But the node.js startup time and loading all the required modules slows down linting times for a single file to ~700 milliseconds. eslint_d reduces this overhead by running a server in the background. It brings the linting time down to ~160 milliseconds. If you want to lint from within your editor whenever you save a file, eslint_d is for you.

Install

This will install the eslint_d command globally:

$ npm install -g eslint_d

Usage

To start the server and lint a file, just run:

$ eslint_d file.js

On the initial call, the eslint_d server is launched and then the given file is linted. Subsequent invocations are super fast.

How does this work?

The first time you use eslint_d, a little server is started in the background and bound to a random port. The port number is stored along with a token in ~/.eslint_d. You can then run eslint_d commands the same way you would use eslint and it will delegate to the background server. It will load a separate instance of eslint for each working directory to make sure settings are kept local. If eslint is found in the current working directories node_modules folder, then this version of eslint is going to be used. Otherwise, the version of eslint that ships with eslint_d is used as a fallback.

However, the performance gain comes at a small price: Changes in the eslint settings are only picked up after a server restart, so you will have to remember to run eslint_d restart after tweaking this rule or installing that plugin. Also, when you have a lot of projects that use eslint, it might use quite a bit of ram for cached instances. All memory can be freed up by running eslint_d stop or eslint_d restart.

Commands

Control the server like this:

$ eslint_d <command>

Available commands:

• start: start the server
• stop: stop the server
• status: print out whether the server is currently running
• restart: restart the server
• [options] file.js [file.js] [dir]: invoke eslint with the given options. The eslint engine will be created in the current directory. If the server is not yet running, it is started.

Type eslint_d --help to see the supported eslint options.

eslint_d will select a free port automatically and store the port number along with an access token in ~/.eslint_d.

Editor integration

Linting

• Sublime: Check out SublimeLinter-contrib-eslint_d.

• Vim: Install the syntastic plugin, then make sure this is in your .vimrc:

  let g:syntastic_javascript_checkers = ['eslint']
  let g:syntastic_javascript_eslint_exec = 'eslint_d'
  

• WebStorm: Configure your IDE to point to the eslint_d package instead of eslint. In the ESLint configuration dialog, under 'ESLint package', select your eslint_d package.

• Atom: You will not gain any performance from this module as it already avoids starting a new node instance and uses the API directly (see this AtomLinter issue).

• Emacs: Use flycheck with the javascript-eslint checker:

  (setq flycheck-javascript-eslint-executable "eslint_d")
  

If you're using eslint_d in any other editor, please tell me!

Automatic Fixing

eslint_d has an additional flag that eslint does not have, --fix-to-stdout which prints the fixed file to stdout. This allows editors to add before save hooks to automatically fix a file prior to saving. It must be used with --stdin.

• Emacs: Add this to your init.el, be sure to add hooks for the actual major modes you use. If you're using along with flycheck, you can replace "eslint_d" below with flycheck-javascript-eslint-executable:

  (defun eslint-fix ()
    (interactive)
    (let ((current-point (point))
          (line (count-screen-lines (window-start) (point)))
          (command (concat
                    "eslint_d"
                    " --stdin"
                    " --fix-to-stdout"
                    " --stdin-filename " buffer-file-name))
          (buffer (current-buffer))
          (text (buffer-substring-no-properties (point-min) (point-max))))
      (with-temp-buffer
        (insert text)
        (when (eq 0
                  (shell-command-on-region
                   ;; Region
                   (point-min)
                   (point-max)
                   ;; Command
                   command
                   ;; Output to current buffer
                   t
                   ;; Replace buffer
                   t
                   ;; Error buffer name
                   "*eslint-fix error*"))
          (let ((fixed-text (buffer-substring-no-properties (point-min) (point-max))))
            (with-current-buffer buffer
              (delete-region (point-min) (point-max))
              (insert fixed-text)
              ;; Restore point and scroll position
              (goto-char current-point)
              (recenter (- line 1))))))))
  
  (add-hook 'js-mode-hook
            (lambda () (add-hook 'before-save-hook #'eslint-fix nil t)))
  

Moar speed

If you're really into performance and want the lowest possible latency, talk to the eslint_d server with netcat. This will also eliminate the node.js startup time.

$ PORT=`cat ~/.eslint_d | cut -d" " -f1`
$ TOKEN=`cat ~/.eslint_d | cut -d" " -f2`
$ echo "$TOKEN $PWD file.js" | nc localhost $PORT

This runs eslint in under 50ms!

Tip For additional speed, did you know that you can lint only files that have changed? This is a feature of normal eslint, but it also works from eslint_d. Run:

$ eslint_d . --cache

Compatibility

• 4.0.0: eslint 3.0+
• 3.0.0: eslint 2.2+
• 1.0.0, 2.0.0: eslint 1.4+

License

MIT

Changelog

4.2.1

Fix [--fix-to-stdout when used with an empty file][pull 59].