ECMAScript code beautifier/formatter


ECMAScript code beautifier/formatter.

Live preview: lloiser/esformatter-visualize

This tool is still on early development and is missing support for many important features.

We are looking for contributors!! doesn't have enough options and not all IDEs/Editors have a good JavaScript code formatter. I would like to have a command line tool (and standalone lib) as powerful/flexible as the WebStorm and FDT code formatters.

This tool could also be reused by other node.js libs like escodegen to format the output (so each lib has a single responsibility).

For more reasoning behind it and history of the project see: esformatter & rocambole

This tool uses rocambole (based on Esprima) to recursively parse the tokens and transform it in place.

  • granular control about white spaces, indent and line breaks.
  • command line interface (cli).
  • be non-destructive.
  • support for local/global config file so settings can be shared between team members.
  • presets for the most popular style guides (Google, jQuery, Idiomatic.js).
  • be the best JavaScript code formatter.

format() method receives a string containing the code that you would like to format and the configuration options that you would like to use and returns a string with the result.

var esformatter = require('esformatter');
// for a list of available options check "lib/preset/default.json" 
var options = {
    // inherit from the default preset 
    preset : 'default',
    indent : {
        value : '  '
    lineBreak : {
        before : {
            // at least one line break before BlockStatement 
            BlockStatement : '>=1',
            // only one line break before BlockStatement 
            DoWhileStatementOpeningBrace : 1,
            // ... 
    whiteSpace : {
        // ... 
var fs = require('fs');
var codeStr = fs.readFileSync('path/to/js/file.js').toString();
// return a string with the formatted code 
var formattedCode = esformatter.format(codeStr, options);

or you can use the transform() method to manipulate an AST in place (allows pipping other tools that manipulates the AST). - so far only supports rocambole generated ASTs, but we will work to fix this limitation in the future (see issue #86).

var inputAST = rocambole.parse('var foo=123;');
// you can also pass the formatting options as second argument like the 
// `format` method 
var outputAST = esformatter.transform(inputAST);
assert(outputAST === inputAST, 'edits AST in place');
assert(outputAST.toString() === 'var foo = 123;', 'formats input');

Used by task runners and/or plugin authors to retrieve the configuration stored on .esformatter and package.json files relative to the filePath, cwd or global config file (~/.esformatter) if it can't find any config file until the root path.

You can also pass an object with customOptions to override the default options.

rc will merge the options from multiple config files.

// will start search from the "foo/bar" directory 
var baseConfig = esformatter.rc('foo/bar/baz.js');
// will start the search from cwd 
var otherConfig = esformatter.rc();
// merge some custom options to the user settings 
var override = esformatter.rc({
  indent: { value: '\t' }

Register a plugin module.

var plugin = {
  nodeAfterfunction(node) {
    // called once for each node, after the esformatter manipulation 

Remove plugin from the execution queue.


Remove all the registered plugins from the execution queue; useful in case you want to edit multiple files using different plugins each time.

You can also use the simple command line interface to process stdin and stdout or read from a file.

npm install -g esformatter
esformatter [OPTIONS] [FILES]
  -c, --config   Path to custom configuration file.
  -p, --preset   Set style guide preset ("jquery""default").
  -h, --help     Display help and usage details.
  -v, --version  Display the current version.
# format "test.js" and output result to stdout 
esformatter test.js
# you can also pipe other shell commands (read file from stdin) 
cat test.js | esformatter
# format "test.js" using options in "options.json" and output result to stdout 
esformatter --config options.json test.js
# process "test.js" and writes to "test.out.js" 
esformatter test.js > test.out.js
# you can override the default settings, see lib/preset/default.json for 
# a list of available options 
esformatter test.js --indent.value="\t" --lineBreak.before.IfStatementOpeningBrace=0

For a live preview check esformatter-visualize

esformatter will look for the closest .esformatter file and use that as a setting unless you specify --preset or --config.

You also have the option to put your esformatter settings inside the package.json file under the esformatter property.

Settings from multiple files will be merged until it finds a config file that contains the property "preset" or "root": true; that makes it easy to define exceptions to the project rules without needing to copy all the shared properties. - for an example see test files inside the "test/compare/rc" folder.

The "preset" property is used to set the prototype of the config file, enabling inheritance. For instance, you can say your config inherits from the jquery preset and only override the settings you need:

  "preset": "jquery",
  "indent": {
    "value": "  "

PS: the jQuery preset is still under development.

Configuration in esformatter consists of three main building blocks:

Indent is responsible for whitespace at the front of each line. indent.value is used for each indentation. The default indents with two spaces. Setting indent.value to "\t" will switch to indentation using tabs.

The other properties for indent toggle indentation for specific elements. These all refer to regular JavaScript statements except for TopLevelFunctionBlock. This is enabled by default, with no special behaviour. When disabled (set to 0), esformattter will not indent top level function blocks (used by the jQuery preset).

Both of these have value, before and after properties. lineBreak's value is "\n" by default, while whiteSpace uses a single space (" "). Its unlikely that you ever need to change these.

More interesting are all the properties nested under before and after. These refer to various elements of JavaScript syntax, where the terms mostly match the names used by the Abstract Syntax Tree (AST) for JavaScript. A lot of them have "...Opening", "...Closing", "...OpeningBrace" and "...ClosingBrace" as variants, allowing very fine grained control over each settings.

Documenting each property here wouldn't be practical. For now we recommend you look at the existing presets (default and jquery) to find the properties you need to adjust for your specific needs. Better yet, adopt one of the presets to avoid having to configure anything beyond the most basic settings (like indent.value).

For lineBreak you can use ranges or integers:

  • positive integer (1 till 99): "add or keep [n] line breaks".
  • -1: keep original line breaks.
  • ">2": add linebreaks until it's over 2.
  • ">=1": add line breaks until it's equal or greater than 1.
  • "<2": remove linebreaks until it's smaller than 2.
  • "<=1": remove/add line breaks until it's smaller or equal to 1.

For whiteSpace you can only use positive integers for now (any positive number between 1 and 99) or -1 when you want to keep the original value.

Esformatter also have support for plugins (v0.2.0+).

JavaScript is a very flexible language, which means people write it in many different ways, since adding support for every single kind of style would be impossible, we decided to introduce plugins; that should give enough flexibility to tailor the formatting to match the craziest needs.

Plugins are automatically loaded from node_modules if you pass the module id in the config file:

  "indent": {
    "value": "\t"
  "plugins": ["esformatter-sample-plugin", "foobar"]

List of plugins and plugins wish list:

You also have the option to register a plugin programmatically:

var plugin = {
  nodeAfterfunction(node) {
    // transform node here 

Plugins are executed in the same order as they are registered (first in, first out).

The plugin methods are executed on the following order: stringBefore > tokenBefore > nodeBefore > nodeAfter > tokenAfter > transform > stringAfter.

All plugin methods are optional.

protip: You can use rocambole-token and rocambole-node to simplify the AST manipulation process.

Called once before any manipulation, the object is shared with the esformatter which means you can use this method to override default options if needed.

var options;
plugin.setOptions = function(opts) {
  // override the default settings (objects are passed by reference, changing 
  // the value here will also change the value used by esformatter) 
  opts.indent.value = '  ';
  // store the options to be used later 
  options = opts;

A way to replace the input string, it should ALWAYS return a string.

plugin.stringBefore = function(str) {
  // prepend a variable declaration to the file 
  return 'var foo = "bar";\n' + str;

Replaces the output string.

PS: using regular expressions or string manipulation methods to process code is very error-prone! BEWARE!

plugin.stringAfter = function(str) {
  // replaces all the occurances of "foo" with "bar" (very naive) 
  return str.replace(/foo/g, 'bar');

Called once for each token (eg. Keyword, Punctuator, WhiteSpace, Indent...) before processing the nodes. Can be used to manipulate the token value or add/remove/replace the token or tokens around it.

var tk = require('rocambole-token');
plugin.tokenBefore = function(token) {
  if (tk.isSemiColon(token) && tk.isSemiColon( {
    // remove semicolon if next token is also a semicolon 

Called once for each token (eg. Keyword, Punctuator, WhiteSpace, Indent...) after processing all the nodes. Can be used to manipulate the token value or add/remove/replace the token or tokens around it.

Called once for each node of the program (eg. VariableDeclaration, IfStatement, FunctionExpression...) before the esformatter default manipulations.

Called once for each node of the program (eg. VariableDeclaration, IfStatement, FunctionExpression...) after the esformatter default manipulations.

var tk = require('rocambole-token');
plugin.nodeAfter = function(node) {
  if (node.type === 'FunctionExpression' || node.type === 'FunctionDeclaration') {
    if (node.body) {
      // insert a line break before the function body 
      tk.before(node.body.startToken, {
        type: 'LineBreak',
        value: options.lineBreak.value

Called before esformatter loops through all the nodes, allows plugin authors to modify the AST before esformatter. This is the ideal place to add/replace nodes.

Called after all nodes and tokens are processed, allows overriding all the changes (including indentation).

var rocambole = require('rocambole');
plugin.transformAfter = function(ast) {
  // if you need to manipulate multiple nodes you can use the 
  // rocambole.moonwalk or rocambole.recusive methods. we don't do it 
  // automatically since you might have very specific needs 
  rocambole.moonwalk(ast, function(node) {

We have an IRC channel #esformatter on for quick discussions about the project development/structure.

See project Wiki for more info:


Released under the MIT license