For formatting, searching, and rewriting JavaScript.
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Latest commit 2ad2ff4 Feb 3, 2016


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For formatting, searching, and rewriting JavaScript. Analogous to gofmt.


npm install -g jsfmt


$ jsfmt --help
  jsfmt [--no-format] [--save-ast] [--diff|--list|--write] [--validate] [--rewrite PATTERN|--search PATTERN] [--json|--ast] [<file>...]
  jsfmt (--version | --help)

  -h --help                      Show this help text
  --version                      Show jsfmt version
  -d --diff                      Show diff against original file
  -l --list                      List the files which differ from jsfmt output
  -v --validate                  Validate the input file(s)
  --no-format                    Do not format the input file(s)
  -w --write                     Overwrite the original file with jsfmt output
  -j --json                      Tell jsfmt that the file being parsed is json
  -a --ast                       Tell jsfmt that the file being parsed is in JSON AST
  --save-ast                     Output the resulting js in JSON AST format
  -r=PATTERN --rewrite PATTERN   Rewrite rule (e.g., 'a.slice(b, len(a) -> a.slice(b)')
  -s=PATTERN --search PATTERN    Search rule (e.g., 'a.slice')

If no path is given it will read from stdin. A directory path will recurse over all *.js files in the directory.

Note that the AST options (--ast and --save-ast) are experimental and may be removed.


For formatting jsfmt uses esformatter.


Any of the esformatter formatting options can be overwritten via a .jsfmtrc file. The file is parsed using rc, which accepts either a json or ini formatted file.

A .jsfmtrc will be read if it exists in any of the following directories:

  • a local .jsfmtrc or the first found looking in ./ ../ ../../ ../../../ etc.
  • $HOME/.jsfmtrc
  • $HOME/.jsfmt/config
  • $HOME/.config/jsfmt
  • $HOME/.config/jsfmt/config
  • /etc/jsfmtrc
  • /etc/jsfmt/config

jsfmt will also attempt to pickup and use the configured indent variable from your .jshintrc configuration file, if present.


The --rewrite flag allows rewriting portions of the JavaScript's AST before formatting. This is especially handy for intelligent renaming and handling API changes from a library. The rewrite rule must be a string of the form:

pattern -> replacement

Both pattern and replacement must be valid JavaScript. In pattern, single-character lowercase identifiers serve as wildcards matching arbitrary expressions; those expressions will be substituted for the same identifiers in the replacement.


Rewrite occurences of _.reduce to use native reduce:

jsfmt --rewrite "_.reduce(a, b, c) -> a.reduce(b, c)" reduce.js


The --search flag allows searching through a JavaScript's AST. The search rule is very similar to the rewrite rule but just outputs expressions that match the given search expression. The search expression must be valid JavaScript.


Find occurences of _.reduce:

jsfmt --search "_.reduce(a, b, c)" reduce.js


The --validate flag will print any errors found by esprima while parsing the JavaScript.


jsfmt --validate bad.js



jsfmt.format(<javascript_string>, <config_object>) // Returns formatted JavaScript
jsfmt.formatJSON(<JSON_string>, <config_object>) // Returns formatted JSON
var config = jsfmt.getConfig(); // Loads the jsfmt config from the appropriate rc file or default config object


var jsfmt = require('jsfmt');
var fs = require('fs');

var js = fs.readFileSync('unformatted.js');
var config = jsfmt.getConfig();

js = jsfmt.format(js, config);


jsfmt.rewrite(<javascript_string>, <rewrite_rule>) // Returns rewritten JavaScript


var jsfmt = require('jsfmt');
var fs = require('fs');

var js = fs.readFileSync('each.js');

js = jsfmt.rewrite(js, "_.each(a, b) -> a.forEach(b)");

Searching<javascript_string>, <search_expression>) // Returns array of matches


var jsfmt = require('jsfmt');
var fs = require('fs');

var js = fs.readFileSync('component.js');, "R.Component.create(a, { dependencies: z })").forEach(function(matches, wildcards) {


jsfmt.validate(<javascript_string>) // Returns errors found while parsing JavaScript
jsfmt.validateJSON(<JSON_string>) // Returns errors found while parsing JSON


var jsfmt = require('jsfmt');
var fs = require('fs');

var js = fs.readFileSync('each.js');
var errors = jsfmt.validate(js);

for (var i = 0; i < errors.length; i++) {


Since jsfmt uses esformatter under the covers for formatting your code you can utilize any esformatter plugins with jsfmt. Please see for more information.


There exists a plugin esformatter-jsx which provides support for formatting JSX with esformatter. Please see for more information on setting up with jsfmt.




  • Added two new command-line args for AST formatting. Note that these are experimental and may be removed.
  • Removed --config option in favor of .jsfmtrc and better docs around rc.
  • Updated esformatter and using new esformatter plugin for automatic brace insertion.
  • Updated style guide to include esformatter changes.
  • Fixes and cleanup for shebang.
  • Support for variable arguments using ES6 rest syntax.
  • General rewrite cleanup.
  • Changing exit code to -1 on missing arg failure.
  • Updates to rc and other dependencies.


  • Adding support for UnaryExpression
  • Fixing bug where rewrite types were not being set properly


  • Fixed bug when searching for expressions within BlockStatement or Program body
  • Added JSON support


  • Added tests
  • Added Gruntfile for development
  • Added CI support
  • Added style guide
  • Added default formatting config
  • Exposed jsfmt.getConfig api method for loading jsfmt config
  • Exposed jsfmt.format(js[, options]) api method for formatting
  • Added --validate option and exposed jsfmt.validate api method
  • Pinned dependencies


  • Add rc and --config config.json support for formatting configuration
  • Making --format the default action
  • Fix support for shebang at the top of js files, e.g. #!/usr/bin/env node
  • Fix jsfmt diff mode where whitespace was unaccounted for due to -b git diff option


  • Initial release


Apache License, Version 2.0. Copyright 2014 Rdio, Inc.