Runs eslint in a background process to improve linting time while editing. On a MacBook Air M1 with node.js v22.2.0 and eslint v9.8.0:

❯ eslint file.js # ~500ms
❯ eslint_d file.js # ~115ms

Features

• Supports all eslint versions from v4 to v9.
• Supports all LTS versions of node.js.
• Automatically starts, stops and restarts the background server.
• Binds to parent process, editor process or exits after IDLE time.
• Falls back to bundled eslint if local eslint is missing.

Setup

❯ npm i -g eslint_d

Vim

• With ale:

  let $ESLINT_D_PPID = getpid()
  let g:ale_javascript_eslint_executable = 'eslint_d'
  let g:ale_javascript_eslint_use_global = 1

• With syntastic:

  let $ESLINT_D_PPID = getpid()
  let g:syntastic_javascript_checkers = ['eslint']
  let g:syntastic_javascript_eslint_exec = 'eslint_d'

Neovim

• With nvim-lint

  vim.env.ESLINT_D_PPID = vim.fn.getpid()
  require('lint').linters_by_ft = {
    javascript = {'eslint_d'},
    typescript = {'eslint_d'},
  }

Emacs

Use flycheck with the javascript-eslint checker:

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

Sublime

The official SublimeLinter-eslint plugin automatically prefers eslint_d if it finds one.

Atom, VSCode, WebStorm

You will not gain any performance from this module as these editors already cache eslint instances for you.

If you're using eslint_d in any other editor, please let us know!

Commands

eslint_d is a drop-in replacement for eslint. It forwards all arguments to eslint and starts the background server if necessary:

eslint_d [options] file.js [file.js] [dir]

All arguments are passed to eslint, except for the following commands:

  start           Start the daemon
  stop            Stop the daemon
  restart         Restart the daemon
  status          Show daemon status, process id and resolved eslint version
  --help, -h      Show this help
  --version, -v   Show version number of eslint_d and bundled eslint
  --fix-to-stdout Print fixed file to stdout (requires --stdin)

Environment variables

• ESLINT_D_PPID Parent process id to monitor. If the parent process dies, the daemon exits as well. "0" disables monitoring (default), and "auto" monitors the parent process that started eslint_d.
• ESLINT_D_IDLE Number of minutes of inactivity before the daemon exits. Defaults to "0" if ESLINT_D_PPID is set, otherwise "15".
• ESLINT_D_MISS How to behave if local eslint is missing. "fallback" uses the bundled eslint (default). "fail" logs an error and exits with code 1. "ignore" silently exits with code 0.
• ESLINT_D_ROOT Provide specific directory to search for node_modules/eslint. Useful in monorepos where node_modules might be in a location other than the project root.

Automatic fixing

eslint_d has an additional option 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.

Vim

Add this to your .vimrc to lint the current buffer or visual selection on <leader>f:

" Autofix entire buffer with eslint_d:
nnoremap <leader>f mF:%!eslint_d --stdin --fix-to-stdout --stdin-filename %<CR>`F
" Autofix visual selection with eslint_d:
vnoremap <leader>f :!eslint_d --stdin --fix-to-stdout<CR>gv

Emacs

See eslintd-fix

How does this work?

eslint_d starts a background server that runs eslint in a separate process. It communicates with the server over a Unix domain socket. When you run eslint_d, it forwards all arguments to the server and prints the result. This is faster because node.js doesn't have to load all the required modules every time.

By default, eslint_d uses the local eslint package if available. If the local eslint package is missing, eslint_d falls back to the bundled eslint package. You can change this behavior with the ESLINT_D_MISS environment variable. To see which eslint package is used, run eslint_d status.

A .eslint_d file is stored in the resolved eslint installation directory which stores a security token, the server port and process id, and the hash of the monitored files. If the file is removed, the server exits.

The server automatically stops after 15 minutes of inactivity. You can change this with the ESLINT_D_IDLE environment variable. Alternatively, you can bind the lifetime of the server to a parent process by setting ESLINT_D_PPID to "auto" or a specific parent process id. The server will exit when the parent process dies. Note that "auto" uses the parent process that started eslint_d, which may not be the editor process.

The server is also automatically restarted if one of the following files changed: package.json, package-lock.json, npm-shrinkwrap.json, yarn.lock, pnpm-lock.yaml.

Debug mode

Added in v14.2.0.

Pass the --debug flag to eslint_d to enable debug output. Use the DEBUG environment variable to limit debug output to eslint_d:

❯ DEBUG="eslint_d:*"

For server side debug output, restart with --debug in a separate terminal:

❯ eslint_d restart --debug # eslint and eslint_d logs
❯ DEBUG="eslint_d:*" eslint_d restart --debug # eslint_d logs only

This will keep the process attached to the terminal and print debug output.

Compatibility

• 14.0.0: eslint 4 - 9, node 18 - 22 (ships with eslint 9) (see [^1])
• 13.0.0: eslint 4 - 8, node 12 - 20 (ships with eslint 8)
• 12.0.0: eslint 4 - 8, node 12 - 16 (ships with eslint 8)
• 11.0.0: eslint 4 - 8, node 12 - 16 (ships with eslint 7)
• 10.0.0: eslint 4 - 7, node 10 - 14 (using new ESLint API if available)
• 9.0.0: eslint 4 - 7, node 10 - 14 (using CLIEngine API)
• 8.0.0: eslint 4 - 6, node 8 - 12
• 7.2.0: eslint 4 - 5, node 6 - 10
• 7.0.0: eslint 5.4+, node 6, 8 and 10
• 6.0.0: eslint 5.0+, node 6+ (eslint dropped node 4)
• 5.0.0: eslint 4.0+
• 4.0.0: eslint 3.0+, node 4+ (eslint dropped node 0.10 and 0.12)
• 3.0.0: eslint 2.2+
• 1.0.0, 2.0.0: eslint 1.4+, node 4 (and probably older)

License

MIT

[^1]: The support for --fix-to-stdout is only provided with eslint 5 and beyond.