# Prettier [![Gitter](https://badges.gitter.im/gitterHQ/gitter.svg)](https://gitter.im/jlongster/prettier) [![Build Status](https://travis-ci.org/prettier/prettier.svg?branch=master)](https://travis-ci.org/prettier/prettier) [![NPM version](https://img.shields.io/npm/v/prettier.svg)](https://www.npmjs.com/package/prettier) - [Usage](#usage) * [CLI](#cli) + [Pre-commit hook for changed files](#pre-commit-hook-for-changed-files) * [API](#api) * [Options](#options) * [Excluding code from formatting](#excluding-code-from-formatting) - [Editor Integration](#editor-integration) * [Atom](#atom) * [Emacs](#emacs) * [Vim](#vim) + [Other `autocmd` events](#other-autocmd-events) + [Customizing Prettier in Vim](#customizing-prettier-in-vim) + [Running Prettier manually in Vim](#running-prettier-manually-in-vim) * [Visual Studio Code](#visual-studio-code) * [Visual Studio](#visual-studio) * [Sublime Text](#sublime-text) * [JetBrains](#jetbrains) - [Language Support](#language-support) - [Related Projects](#related-projects) - [Technical Details](#technical-details) - [Badge](#badge) - [Contributing](#contributing) Prettier is an opinionated JavaScript formatter inspired by [refmt](https://facebook.github.io/reason/tools.html) with advanced support for language features from [ES2017](https://github.com/tc39/proposals/blob/master/finished-proposals.md), [JSX](https://facebook.github.io/jsx/), and [Flow](https://flow.org/). It removes all original styling[\*](#styling-footnote) and ensures that all outputted JavaScript conforms to a consistent style. (See this [blog post](http://jlongster.com/A-Prettier-Formatter)) If you are interested in the details, you can watch those two conference talks: This goes way beyond [ESLint](http://eslint.org/) and other projects [built on it](https://github.com/feross/standard). Unlike ESLint, there aren't a million configuration options and rules. But more importantly: **everything is fixable**. This works because Prettier never "checks" anything; it takes JavaScript as input and delivers the formatted JavaScript as output. In technical terms: Prettier parses your JavaScript into an AST (Abstract Syntax Tree) and pretty-prints the AST, completely ignoring any of the original formatting[\*](#styling-footnote). Say hello to completely consistent syntax! There's an extremely important piece missing from existing styling tools: **the maximum line length**. Sure, you can tell ESLint to warn you when you have a line that's too long, but that's an after-thought (ESLint *never* knows how to fix it). The maximum line length is a critical piece the formatter needs for laying out and wrapping code. For example, take the following code: ```js foo(arg1, arg2, arg3, arg4); ``` That looks like the right way to format it. However, we've all run into this situation: ```js foo(reallyLongArg(), omgSoManyParameters(), IShouldRefactorThis(), isThereSeriouslyAnotherOne()); ``` Suddenly our previous format for calling function breaks down because this is too long. What you would probably do is this instead: ```js foo( reallyLongArg(), omgSoManyParameters(), IShouldRefactorThis(), isThereSeriouslyAnotherOne() ); ``` This clearly shows that the maximum line length has a direct impact on the style of code we desire. The fact that current style tools ignore this means they can't really help with the situations that are actually the most troublesome. Individuals on teams will all format these differently according to their own rules and we lose the consistency we sought after. Even if we disregard line widths, it's too easy to sneak in various styles of code in all other linters. The most strict linter I know happily lets all these styles happen: ```js foo({ num: 3 }, 1, 2) foo( { num: 3 }, 1, 2) foo( { num: 3 }, 1, 2 ) ``` Prettier bans all custom styling[\*](#styling-footnote) by parsing it away and re-printing the parsed AST with its own rules that take the maximum line width into account, wrapping code when necessary. \*_Well actually, some original styling is preserved when practical—see [empty lines] and [multi-line objects]._ [empty lines]:Rationale.md#empty-lines [multi-line objects]:Rationale.md#multi-line-objects ## Usage Install: ``` yarn add prettier --dev ``` You can install it globally if you like: ``` yarn global add prettier ``` *We're defaulting to `yarn` but you can use `npm` if you like:* ``` npm install [-g] prettier ``` ### CLI Run Prettier through the CLI with this script. Run it without any arguments to see the [options](#options). To format a file in-place, use `--write`. You may want to consider committing your code before doing that, just in case. ```bash prettier [opts] [filename ...] ``` In practice, this may look something like: ```bash prettier --single-quote --trailing-comma es5 --write "{app,__{tests,mocks}__}/**/*.js" ``` (Don't forget the quotes around the globs! The quotes make sure that Prettier expands the globs rather than your shell, for cross-platform usage.) In the future we will have better support for formatting whole projects. If you're worried that Prettier will change the correctness of your code, add `--debug-check` to the command. This will cause Prettier to print an error message if it detects that code correctness might have changed. Note that `--write` cannot be used with `--debug-check`. Another useful flag is `--list-different` (or `-l`) which prints the filenames of files that are different from Prettier formatting. If there are differences the script errors out, which is useful in a CI scenario. ```bash prettier --single-quote --list-different "src/**/*.js" ``` #### Pre-commit hook for changed files You can use this with a pre-commit tool. This can re-format your files that are marked as "staged" via `git add` before you commit. ##### 1. [lint-staged](https://github.com/okonet/lint-staged) Install it along with [husky](https://github.com/typicode/husky): ```bash yarn add lint-staged husky --dev ``` and add this config to your `package.json`: ```json { "scripts": { "precommit": "lint-staged" }, "lint-staged": { "*.js": [ "prettier --write", "git add" ] } } ``` See https://github.com/okonet/lint-staged#configuration for more details about how you can configure lint-staged. ##### 2. [pre-commit](https://github.com/pre-commit/pre-commit) Just copy the following config in your pre-commit config yaml file ```yaml - repo: https://github.com/awebdeveloper/pre-commit-prettier sha: '' # Use the sha or tag you want to point at hooks: - id: prettier additional_dependencies: ['prettier@1.1.0'] ``` Find more info from [here](https://github.com/awebdeveloper/pre-commit-prettier) ##### 3. bash script Alternately you can just save this script as `.git/hooks/pre-commit` and give it execute permission: ```bash #!/bin/sh jsfiles=$(git diff --cached --name-only --diff-filter=ACM | grep '\.jsx\?$' | tr '\n' ' ') [ -z "$jsfiles" ] && exit 0 diffs=$(node_modules/.bin/prettier -l $jsfiles) [ -z "$diffs" ] && exit 0 echo "here" echo >&2 "Javascript files must be formatted with prettier. Please run:" echo >&2 "node_modules/.bin/prettier --write "$diffs"" exit 1 ``` ### API The API has two functions, exported as `format` and `check`. `format` usage is as follows: ```js const prettier = require("prettier"); const options = {} // optional prettier.format(source, options); ``` `check` checks to see if the file has been formatted with Prettier given those options and returns a Boolean. This is similar to the `--list-different` parameter in the CLI and is useful for running Prettier in CI scenarios. ### Options Prettier ships with a handful of customizable format options, usable in both the CLI and API. | Option | Default | CLI override | API override | | ------------- | ------------- | ------------- | ------------- | | **Print Width** - Specify the length of line that the printer will wrap on.

We strongly recommend against using more than 80 columns. Prettier works by craming as much content as possible until it reaches the limit, which happens to work well for 80 columns but makes lines that are very crowded. When a bigger column count is used in styleguides, it usually means that code is allowed to go beyond 80 columns, but not to make every single line go there, like prettier would do. | `80` | `--print-width ` | `printWidth: ` | **Tab Width** - Specify the number of spaces per indentation-level. | `2` | `--tab-width ` | `tabWidth: ` | | **Tabs** - Indent lines with tabs instead of spaces. | `false` | `--use-tabs` | `useTabs: ` | | **Semicolons** - Print semicolons at the ends of statements.

Valid options:
- `true` - add a semicolon at the end of every statement
- `false` - only add semicolons at the beginning of lines that may introduce ASI failures | `true` | `--no-semi` | `semi: ` | | **Quotes** - Use single quotes instead of double quotes. | `false` | `--single-quote` | `singleQuote: ` | | **Trailing Commas** - Print trailing commas wherever possible.

Valid options:
- `"none"` - no trailing commas
- `"es5"` - trailing commas where valid in ES5 (objects, arrays, etc)
- `"all"` - trailing commas wherever possible (function arguments). This requires node 8 or a [transform](https://babeljs.io/docs/plugins/syntax-trailing-function-commas/). | `"none"` | --trailing-comma | trailingComma: "" | | **Bracket Spacing** - Print spaces between brackets in object literals.

Valid options:
- `true` - Example: `{ foo: bar }`
- `false` - Example: `{foo: bar}` | `true` | `--no-bracket-spacing` | `bracketSpacing: ` | | **JSX Brackets on Same Line** - Put the `>` of a multi-line JSX element at the end of the last line instead of being alone on the next line | `false` | `--jsx-bracket-same-line` | `jsxBracketSameLine: ` | | **Range Start** - Format code starting at a given character offset. The range will extend backwards to the start of the first line containing the selected statement. | `0` | `--range-start ` | `rangeStart: ` | | **Range End** - Format code ending at a given character offset (exclusive). The range will extend forwards to the end of the selected statement. | `Infinity` | `--range-end ` | `rangeEnd: ` | | **Parser** - Specify which parser to use. Both parsers support the same set of JavaScript features (including Flow). You shouldn't have to change this setting. | `babylon` | --parser | parser: "" | ### Excluding code from formatting A JavaScript comment of `// prettier-ignore` will exclude the next node in the abstract syntax tree from formatting. For example: ```js matrix( 1, 0, 0, 0, 1, 0, 0, 0, 1 ) // prettier-ignore matrix( 1, 0, 0, 0, 1, 0, 0, 0, 1 ) ``` will be transformed to: ```js matrix(1, 0, 0, 0, 1, 0, 0, 0, 1); // prettier-ignore matrix( 1, 0, 0, 0, 1, 0, 0, 0, 1 ) ``` ## Editor Integration ### Atom Atom users can simply install the [prettier-atom](https://github.com/prettier/prettier-atom) package and use `Ctrl+Alt+F` to format a file (or format on save if enabled). ### Emacs Emacs users should see [this directory](https://github.com/prettier/prettier/tree/master/editors/emacs) for on-demand formatting. ### Vim Add [sbdchd](https://github.com/sbdchd)/[neoformat](https://github.com/sbdchd/neoformat) to your list based on the tool you use: ```vim Plug 'sbdchd/neoformat' ``` Then make Neoformat run on save: ```vim autocmd BufWritePre *.js Neoformat ``` #### Other `autocmd` events You can also make Vim format your code more frequently, by setting an `autocmd` for other events. Here are a couple of useful ones: * `TextChanged`: after a change was made to the text in Normal mode * `InsertLeave`: when leaving Insert mode For example, you can format on both of the above events together with `BufWritePre` like this: ```vim autocmd BufWritePre,TextChanged,InsertLeave *.js Neoformat ``` See `:help autocmd-events` in Vim for details. #### Customizing Prettier in Vim If your project requires settings other than the default Prettier settings, you can pass arguments to do so in your `.vimrc` or [vim project](http://vim.wikia.com/wiki/Project_specific_settings), you can do so: ```vim autocmd FileType javascript setlocal formatprg=prettier\ --stdin\ --parser\ flow\ --single-quote\ --trailing-comma\ es5 " Use formatprg when available let g:neoformat_try_formatprg = 1 ``` Each option needs to be escaped with `\`. #### Running Prettier manually in Vim If you need a little more control over when prettier is run, you can create a custom key binding. In this example, `gp` (mnemonic: "get pretty") is used to run prettier (with options) in the currently active buffer: ```vim nnoremap gp :silent %!prettier --stdin --trailing-comma all --single-quote ``` ### Visual Studio Code Can be installed using the extension sidebar. Search for `Prettier - JavaScript formatter`. Can also be installed using `ext install prettier-vscode`. [Check its repository for configuration and shortcuts](https://github.com/esbenp/prettier-vscode) ### Visual Studio Install the [JavaScript Prettier extension](https://github.com/madskristensen/JavaScriptPrettier). ### Sublime Text Sublime Text support is available through Package Control and the [JsPrettier](https://packagecontrol.io/packages/JsPrettier) plug-in. ### JetBrains JetBrains users can configure `prettier` as an **External Tool**. See [this blog post](https://blog.jetbrains.com/webstorm/2016/08/using-external-tools/) or [this directory](https://github.com/jlongster/prettier/tree/master/editors/jetbrains) with examples. More editors are coming soon. ## Language Support Prettier attempts to support all JavaScript language features, including non-standardized ones. By default it uses the [Babylon](https://github.com/babel/babylon) parser with all language features enabled, but you can also use the [Flow](https://github.com/facebook/flow) parser with the `parser` API or `--parser` CLI [option](#options). All of JSX and Flow syntax is supported. In fact, the test suite in `tests` *is* the entire Flow test suite and they all pass. ## Related Projects - [`eslint-plugin-prettier`](https://github.com/prettier/eslint-plugin-prettier) plugs Prettier into your ESLint workflow - [`eslint-config-prettier`](https://github.com/prettier/eslint-config-prettier) turns off all ESLint rules that are unnecessary or might conflict with Prettier - [`prettier-eslint`](https://github.com/prettier/prettier-eslint) passes `prettier` output to `eslint --fix` - [`prettier-standard`](https://github.com/sheerun/prettier-standard) uses `prettier` and `prettier-eslint` to format code with standard rules - [`prettier-standard-formatter`](https://github.com/dtinth/prettier-standard-formatter) passes `prettier` output to `standard --fix` - [`prettier-miscellaneous`](https://github.com/arijs/prettier-miscellaneous) `prettier` with a few minor extra options - [`neutrino-preset-prettier`](https://github.com/SpencerCDixon/neutrino-preset-prettier) allows you to use Prettier as a Neutrino preset - [`prettier_d`](https://github.com/josephfrazier/prettier_d.js) runs Prettier as a server to avoid Node.js startup delay ## Technical Details This printer is a fork of [recast](https://github.com/benjamn/recast)'s printer with its algorithm replaced by the one described by Wadler in "[A prettier printer](http://homepages.inf.ed.ac.uk/wadler/papers/prettier/prettier.pdf)". There still may be leftover code from recast that needs to be cleaned up. The basic idea is that the printer takes an AST and returns an intermediate representation of the output, and the printer uses that to generate a string. The advantage is that the printer can "measure" the IR and see if the output is going to fit on a line, and break if not. This means that most of the logic of printing an AST involves generating an abstract representation of the output involving certain commands. For example, `concat(["(", line, arg, line ")"])` would represent a concatentation of opening parens, an argument, and closing parens. But if that doesn't fit on one line, the printer can break where `line` is specified. More (rough) details can be found in [commands.md](commands.md). Better docs will come soon. ## Badge Show the world you're using *Prettier* → [![styled with prettier](https://img.shields.io/badge/styled_with-prettier-ff69b4.svg)](https://github.com/prettier/prettier) ```md [![styled with prettier](https://img.shields.io/badge/styled_with-prettier-ff69b4.svg)](https://github.com/prettier/prettier) ``` ## Contributing To get up and running, install the dependencies and run the tests: ``` yarn yarn lint yarn test ``` Here's what you need to know about the tests: * The tests uses [Jest](https://facebook.github.io/jest/) snapshots. * You can make changes and run `jest -u` (or `yarn test -- -u`) to update the snapshots. Then run `git diff` to take a look at what changed. Always update the snapshots when opening a PR. * You can run `AST_COMPARE=1 jest` for a more robust test run. That formats each file, re-parses it, and compares the new AST with the original one and makes sure they are semantically equivalent. * Each test folder has a `jsfmt.spec.js` that runs the tests. Normally you can just put `run_spec(__dirname);` there. You can also pass options and additional parsers, like this: `run_spec(__dirname, { trailingComma: "es5" }, ["babylon"]);` * `tests/flow/` contains the Flow test suite, and is not supposed to be edited by hand. To update it, clone the Flow repo next to the Prettier repo and run: `node scripts/sync-flow-tests.js ../flow/tests/`. * If you would like to debug prettier locally, you can either debug it in node or the browser. The easiest way to debug it in the browser is to run the interactive `docs` REPL locally. The easiest way to debug it in node, is to create a local test file and run it in an editor like VS Code. Run `yarn lint -- --fix` to automatically format files. If you can, take look at [commands.md](commands.md) and check out [Wadler's paper](http://homepages.inf.ed.ac.uk/wadler/papers/prettier/prettier.pdf) to understand how Prettier works.