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Beautify / pretty print JavaScript and JSON

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Beautify / pretty print JavaScript and JSON. Turn really ugly and poorly indented files into masterpieces.

npm version Build Status Dependencies Dev Dependencies


You must have an ECMAScript 5 environment. If you're in a browser or otherwise don't have convenient things like Array.prototype.forEach then you can use es5-shim to patch in the necessary functions.

This also relies on Complexion and ComplexionJS. If you plan on using this in a web browser, I strongly suggest you look into Browserify or a similar technique to bundle up JavaScript.


When you want to run pretty-js from the command line, use npm to install the script globally.

npm install -g pretty-js

If you'd rather call the library directly, then list "pretty-js" as a dependency in your package.json file and let npm install it locally. You can do it easily with npm.

npm install --save-dev pretty-js

Running via Command Line

Did you install this script globally? (npm install -g pretty-js) If so, you now have the boundless power of the JavaScript pretty printer in a convenient command-line interface.

pretty-js [options] [filename ...]

Here are a few typical ways to run the pretty printer.

# Beautify ugly.js
pretty-js ugly.js > pretty.js

# Format JSON
pretty-js -j ugly.json > pretty.json

# Use Windows linefeeds and jslint-compatible rules
# Overwrites original file with formatted content
pretty-js --newline CRLF --jslint --in-place source-code.js

# Rewrite all JavaScript files and display the name of the
# file being changed
pretty-js -i -v *.js

There's a lot of options and you can control all of the aspects of the pretty printer. Use pretty-js --help for a lot of information. Reading from stdin is an option as well, thanks to processFiles. All of the following read from stdin and write to stdout.

cat ugly.js | pretty-js > pretty.js

cat ugly.js | pretty-js - > pretty.js

# The "in-place" editing of stdin just writes to stdout
cat ugly.js | pretty-js -i > pretty.js

Using the API

I find that code examples are very illustrative.

var code, options, prettyJs;

// Load the library
prettyJs = require('pretty-js');

// Let's format some code quickly with the defaults
code = '// some JavaScript code goes in here';
console.log(prettyJs(code));  // Displays formatted code

// Format code and specify a couple options
options = {
    indent: "\t",  // Switch to tabs for indentation
    newline: "\r\n"  // Windows-style newlines
console.log(prettyJs(code, options));


All of these options are also available when using the command-line interface. When there is a difference in the default value, that is explained for each option along with the reasoning behind the difference.

bom (boolean or null)

Always add, remove, or just preserve the BOM (byte order mark) in a file. The BOM can cause problems plus JavaScript and JSON files are expected to typically be in UTF-8.

  • true: Always add a BOM to the file
  • false: Always remove a BOM from the file
  • null: Preserve a BOM if one exists

Defaults to false to help remove problems.

commentSpace (string)

Spaces to the left of single-line comments.

someFunction();  // single-line comment

Defaults to " " (two spaces)

convertStrings ("double", "single", false/null)

Strings can be 'single quoted' or "double quoted". For consistency, the pretty printer will change (and properly re-escape) strings to match your preferred style.

Defaults to double so it works better with JSON.

elseNewline (boolean)

When enabled, put else and catch on a new line. When disabled, those keywords will be on the same line as the previous closing brace.

Defaults to false.

indent (string)

What to use for a single indentation level.

The eternal "spaces vs. tabs" debate comes up a lot.

Defaults to " " (four spaces).

jslint (boolean)

When truthy this uses jslint-compatible rules. For instance, this forces quoteProperties to be false. There's some other changes regarding switch blocks and punctuation as well.

Defaults to false.

newline (string)

This is the string to use for newlines.

  • "\n" is for Mac, Unix and Linux
  • "\r\n" is for Windows
  • "\r" is the old Mac style

Defaults to "\n" (Mac/Unix/Linux style).

noSpaceAfterIf (boolean)

Enabling this option removes the space that would appear in if (.

Defaults to false.

noSpaceAfterFor (boolean)

Enabling this option removes the space that would appear in for (.

Defaults to false.

noSpaceAfterFunction (boolean)

Enabling this option removes the space that would appear in function (. Please note that this is only applied for anonymous functions, not named functions.

Defaults to false.

noSpaceAfterSwitch (boolean)

Enabling this option removes the space that would appear in switch (.

Defaults to false.

noSpaceWithIncDec (boolean)

Enable this option to remove the space between an identifier and the ++ or --.

Defaults to false.

quoteProperties (boolean or null)

Wrap object properties in quotes or remove them.

  • true: Always add quotes around properties
  • false: Always remove quotes around properties when syntactically possible
  • null: Keep quoted properties quoted and unquoted properties unquoted

Defaults to false.

trailingNewline (boolean)

Adds or removes newline at end of file.

  • true: Always add newline to end of file
  • false: Always remove newline from end of file

Defaults to false.


If you want to work on this library, you need to check out the repository and run npm install to get the dependencies.

Tests are always included. Make sure tests cover your changes. To run the current tests, just use npm test or grunt test (they will run the same test suite).


This software is licensed under an MIT license with an additional non-advertising clause.



Package last updated on 19 May 2021

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