eslint_d
Makes eslint the fastest linter on the planet.
"But eslint is pretty fast already, right?"
Yes, it's really 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. 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.
It's possible to force eslint_d
to only resolve local eslint
by setting the
ESLINT_D_LOCAL_ESLINT_ONLY
environment variable to a truthy value (ie. true
or 1
).
To keep the memory footprint low, eslint_d
keeps only the last 10 used
instances in the internal nanolru cache.
What if eslint or a plugin is updated?
The cached version of eslint and the Node require
cache for the current
working directory are cleared whenever a change to one of these files is
detected: package.json
, package-lock.json
, npm-shrinkwrap.json
,
yarn.lock
and pnpm-lock.yaml
. If changes are not automatically detected,
remember to run eslint_d restart
to bounce the background server.
Note: Change detection was switched from mtime to content hash with v12.
Which versions of eslint are supported?
You can use eslint_d
with multiple projects depending on different versions
of eslint. If no local eslint is found, eslint_d
falls back to the eslint
version that ships with eslint_d
.
Commands
Control the server like this:
$ eslint_d <command>
Available commands:
start
: start the serverstop
: stop the serverstatus
: print out whether the server is currently runningrestart
: 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.
When the server starts, eslint_d
selects a free port automatically
and decides on a random access token. Both the port and token are
written to an .eslint_d
file so that future usages of eslint_d
can
connect to the already running server. The .eslint_d
file is stored
under the XDG_RUNTIME_DIR
directory if this environment variable is
defined. If the variable is not defined then the file is stored in the
user's home directory.
Editor integration
Linting
-
Vim:
-
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.
-
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: 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!
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
.
-
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<CR>`F
" Autofix visual selection with eslint_d:
vnoremap <leader>f :!eslint_d --stdin --fix-to-stdout<CR>gv
-
Emacs: See eslintd-fix
-
If the above doesn't autofix: This can happen with .vue files
Change eslint_d --stdin --fix-to-stdout
to eslint_d --stdin --fix-to-stdout --stdin-filename %
(% = path to file you want to autofix)
In Vim, the above mapping should be replaced with:
nnoremap <leader>f mF:%!eslint_d --stdin --fix-to-stdout --stdin-filename %<CR>`F
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.
You first need to extract the port and access token from the
.eslint_d
file. The location of this file may change depending on
your system (see above). For example, if XDG_RUNTIME_DIR
is
specified, you can do this:
$ PORT=`cat $XDG_RUNTIME_DIR/.eslint_d | cut -d" " -f1`
$ TOKEN=`cat $XDG_RUNTIME_DIR/.eslint_d | cut -d" " -f2`
Then, you can do the following to run eslint on file.js
:
$ echo "$TOKEN $PWD file.js" | nc localhost $PORT
Or if you want to work with stdin:
$ echo "$TOKEN $PWD --stdin" | cat - 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
References
If you're interested in building something similar to this: Most of the logic
was extracted to core_d, a library that manages the background server.
Compatibility
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 - 127.2.0
: eslint 4 - 5, node 6 - 107.0.0
: eslint 5.4+, node 6, 8 and 106.0.0
: 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