458 lines
17 KiB
Markdown
458 lines
17 KiB
Markdown
# Prettier
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[![Gitter](https://badges.gitter.im/gitterHQ/gitter.svg)](https://gitter.im/jlongster/prettier)
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[![Build Status](https://travis-ci.org/prettier/prettier.svg?branch=master)](https://travis-ci.org/prettier/prettier)
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[![NPM version](https://img.shields.io/npm/v/prettier.svg)](https://www.npmjs.com/package/prettier)
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<!-- toc -->
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- [Usage](#usage)
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* [CLI](#cli)
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+ [Pre-commit hook for changed files](#pre-commit-hook-for-changed-files)
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* [API](#api)
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* [Options](#options)
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* [Excluding code from formatting](#excluding-code-from-formatting)
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- [Editor Integration](#editor-integration)
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* [Atom](#atom)
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* [Emacs](#emacs)
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* [Vim](#vim)
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+ [Other `autocmd` events](#other-autocmd-events)
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+ [Customizing Prettier in Vim](#customizing-prettier-in-vim)
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+ [Running Prettier manually in Vim](#running-prettier-manually-in-vim)
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* [Visual Studio Code](#visual-studio-code)
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* [Visual Studio](#visual-studio)
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* [Sublime Text](#sublime-text)
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* [WebStorm](#webstorm)
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- [Language Support](#language-support)
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- [Related Projects](#related-projects)
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- [Technical Details](#technical-details)
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- [Badge](#badge)
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- [Contributing](#contributing)
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<!-- tocstop -->
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Prettier is an opinionated JavaScript formatter inspired by
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[refmt](https://facebook.github.io/reason/tools.html) with advanced
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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
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all original styling[\*](#styling-footnote) and ensures that all outputted JavaScript
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conforms to a consistent style. (See this [blog post](http://jlongster.com/A-Prettier-Formatter))
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If you are interested in the details, you can watch those two conference talks:
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<a href="https://www.youtube.com/watch?v=hkfBvpEfWdA"><img width="298" src="https://cloud.githubusercontent.com/assets/197597/24886367/dda8a6f0-1e08-11e7-865b-22492450f10f.png"></a> <a href="https://www.youtube.com/watch?v=0Q4kUNx85_4"><img width="298" src="https://cloud.githubusercontent.com/assets/197597/24886368/ddacd6f8-1e08-11e7-806a-9febd23cbf47.png"></a>
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This goes way beyond [ESLint](http://eslint.org/) and other projects
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[built on it](https://github.com/feross/standard). Unlike ESLint,
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there aren't a million configuration options and rules. But more
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importantly: **everything is fixable**. This works because Prettier
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never "checks" anything; it takes JavaScript as input and delivers the
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formatted JavaScript as output.
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In technical terms: Prettier parses your JavaScript into an AST (Abstract Syntax Tree) and
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pretty-prints the AST, completely ignoring any of the original
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formatting[\*](#styling-footnote). Say hello to completely consistent syntax!
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There's an extremely important piece missing from existing styling
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tools: **the maximum line length**. Sure, you can tell ESLint to warn
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you when you have a line that's too long, but that's an after-thought
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(ESLint *never* knows how to fix it). The maximum line length is a
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critical piece the formatter needs for laying out and wrapping code.
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For example, take the following code:
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```js
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foo(arg1, arg2, arg3, arg4);
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```
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That looks like the right way to format it. However, we've all run
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into this situation:
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```js
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foo(reallyLongArg(), omgSoManyParameters(), IShouldRefactorThis(), isThereSeriouslyAnotherOne());
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```
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Suddenly our previous format for calling function breaks down because
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this is too long. What you would probably do is this instead:
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```js
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foo(
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reallyLongArg(),
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omgSoManyParameters(),
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IShouldRefactorThis(),
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isThereSeriouslyAnotherOne()
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);
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```
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This clearly shows that the maximum line length has a direct impact on
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the style of code we desire. The fact that current style tools ignore
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this means they can't really help with the situations that are
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actually the most troublesome. Individuals on teams will all format
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these differently according to their own rules and we lose the
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consistency we sought after.
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Even if we disregard line widths, it's too easy to sneak in various
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styles of code in all other linters. The most strict linter I know
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happily lets all these styles happen:
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```js
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foo({ num: 3 },
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1, 2)
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foo(
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{ num: 3 },
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1, 2)
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foo(
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{ num: 3 },
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1,
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2
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)
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```
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Prettier bans all custom styling[\*](#styling-footnote) by parsing it away and re-printing
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the parsed AST with its own rules that take the maximum line width
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into account, wrapping code when necessary.
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<a href="#styling-footnote" name="styling-footnote">\*</a>_Well actually, some
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original styling is preserved when practical—see [empty lines] and [multi-line
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objects]._
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[empty lines]:Rationale.md#empty-lines
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[multi-line objects]:Rationale.md#multi-line-objects
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## Usage
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Install:
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```
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yarn add prettier --dev
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```
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You can install it globally if you like:
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```
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yarn global add prettier
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```
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*We're defaulting to `yarn` but you can use `npm` if you like:*
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```
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npm install [-g] prettier
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```
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### CLI
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Run Prettier through the CLI with this script. Run it without any
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arguments to see the [options](#options).
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To format a file in-place, use `--write`. You may want to consider
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committing your code before doing that, just in case.
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```bash
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prettier [opts] [filename ...]
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```
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In practice, this may look something like:
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```bash
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prettier --single-quote --trailing-comma es5 --write "{app,__{tests,mocks}__}/**/*.js"
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```
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Don't forget the quotes around the globs! The quotes make sure that Prettier
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expands the globs rather than your shell, for cross-platform usage.
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The [glob syntax from the glob module](https://github.com/isaacs/node-glob/blob/master/README.md#glob-primer)
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is used.
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Prettier CLI will ignore files located in `node_modules` directory. To opt-out from this behavior use `--with-node-modules` flag.
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If you're worried that Prettier will change the correctness of your code, add `--debug-check` to the command.
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This will cause Prettier to print an error message if it detects that code correctness might have changed.
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Note that `--write` cannot be used with `--debug-check`.
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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.
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```bash
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prettier --single-quote --list-different "src/**/*.js"
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```
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#### Pre-commit hook for changed files
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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.
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##### 1. [lint-staged](https://github.com/okonet/lint-staged)
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Install it along with [husky](https://github.com/typicode/husky):
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```bash
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yarn add lint-staged husky --dev
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```
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and add this config to your `package.json`:
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```json
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{
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"scripts": {
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"precommit": "lint-staged"
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},
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"lint-staged": {
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"*.js": [
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"prettier --write",
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"git add"
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]
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}
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}
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```
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See https://github.com/okonet/lint-staged#configuration for more details about how you can configure lint-staged.
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##### 2. [pre-commit](https://github.com/pre-commit/pre-commit)
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Just copy the following config in your pre-commit config yaml file
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```yaml
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- repo: https://github.com/awebdeveloper/pre-commit-prettier
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sha: '' # Use the sha or tag you want to point at
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hooks:
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- id: prettier
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additional_dependencies: ['prettier@1.3.1']
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```
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Find more info from [here](https://github.com/awebdeveloper/pre-commit-prettier)
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##### 3. bash script
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Alternately you can just save this script as `.git/hooks/pre-commit` and give it execute permission:
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```bash
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#!/bin/sh
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jsfiles=$(git diff --cached --name-only --diff-filter=ACM | grep '\.jsx\?$' | tr '\n' ' ')
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[ -z "$jsfiles" ] && exit 0
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diffs=$(node_modules/.bin/prettier -l $jsfiles)
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[ -z "$diffs" ] && exit 0
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echo "here"
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echo >&2 "Javascript files must be formatted with prettier. Please run:"
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echo >&2 "node_modules/.bin/prettier --write "$diffs""
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exit 1
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```
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### API
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The API has two functions, exported as `format` and `check`. `format` usage is as follows:
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```js
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const prettier = require("prettier");
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const options = {} // optional
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prettier.format(source, options);
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```
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`check` checks to see if the file has been formatted with Prettier given those options and returns a Boolean.
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This is similar to the `--list-different` parameter in the CLI and is useful for running Prettier in CI scenarios.
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### Options
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Prettier ships with a handful of customizable format options, usable in both the CLI and API.
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| Option | Default | CLI override | API override |
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| ------------- | ------------- | ------------- | ------------- |
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| **Print Width** - Specify the length of line that the printer will wrap on.<br /><br /><strong>We strongly recommend against using more than 80 columns</strong>. 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 <int>` | `printWidth: <int>`
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| **Tab Width** - Specify the number of spaces per indentation-level. | `2` | `--tab-width <int>` | `tabWidth: <int>` |
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| **Tabs** - Indent lines with tabs instead of spaces. | `false` | `--use-tabs` | `useTabs: <bool>` |
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| **Semicolons** - Print semicolons at the ends of statements.<br /><br />Valid options: <br /> - `true` - add a semicolon at the end of every statement <br /> - `false` - only add semicolons at the beginning of lines that may introduce ASI failures | `true` | `--no-semi` | `semi: <bool>` |
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| **Quotes** - Use single quotes instead of double quotes. | `false` | `--single-quote` | `singleQuote: <bool>` |
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| **Trailing Commas** - Print trailing commas wherever possible.<br /><br />Valid options: <br /> - `"none"` - no trailing commas <br /> - `"es5"` - trailing commas where valid in ES5 (objects, arrays, etc) <br /> - `"all"` - trailing commas wherever possible (function arguments). This requires node 8 or a [transform](https://babeljs.io/docs/plugins/syntax-trailing-function-commas/). | `"none"` | <code>--trailing-comma <none|es5|all></code> | <code>trailingComma: "<none|es5|all>"</code> |
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| **Bracket Spacing** - Print spaces between brackets in object literals.<br /><br />Valid options: <br /> - `true` - Example: `{ foo: bar }` <br /> - `false` - Example: `{foo: bar}` | `true` | `--no-bracket-spacing` | `bracketSpacing: <bool>` |
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| **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: <bool>` |
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| **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 <int>` | `rangeStart: <int>` |
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| **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 <int>` | `rangeEnd: <int>` |
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| **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` | <code>--parser <flow|babylon></code> | <code>parser: "<flow|babylon>"</code> |
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### Excluding code from formatting
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A JavaScript comment of `// prettier-ignore` will exclude the next node in the abstract syntax tree from formatting.
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For example:
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```js
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matrix(
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1, 0, 0,
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0, 1, 0,
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0, 0, 1
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)
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// prettier-ignore
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matrix(
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1, 0, 0,
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0, 1, 0,
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0, 0, 1
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)
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```
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will be transformed to:
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```js
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matrix(1, 0, 0, 0, 1, 0, 0, 0, 1);
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// prettier-ignore
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matrix(
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1, 0, 0,
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0, 1, 0,
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0, 0, 1
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)
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```
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## Editor Integration
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### Atom
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Atom users can simply install the [prettier-atom](https://github.com/prettier/prettier-atom) package and use
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`Ctrl+Alt+F` to format a file (or format on save if enabled).
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### Emacs
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Emacs users should see [this directory](https://github.com/prettier/prettier/tree/master/editors/emacs)
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for on-demand formatting.
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### Vim
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Add [sbdchd](https://github.com/sbdchd)/[neoformat](https://github.com/sbdchd/neoformat) to your list based on the tool you use:
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```vim
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Plug 'sbdchd/neoformat'
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```
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Then make Neoformat run on save:
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```vim
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autocmd BufWritePre *.js Neoformat
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```
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#### Other `autocmd` events
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You can also make Vim format your code more frequently, by setting an `autocmd` for other events. Here are a couple of useful ones:
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* `TextChanged`: after a change was made to the text in Normal mode
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* `InsertLeave`: when leaving Insert mode
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For example, you can format on both of the above events together with `BufWritePre` like this:
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```vim
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autocmd BufWritePre,TextChanged,InsertLeave *.js Neoformat
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```
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See `:help autocmd-events` in Vim for details.
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#### Customizing Prettier in Vim
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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:
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```vim
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autocmd FileType javascript setlocal formatprg=prettier\ --stdin\ --parser\ flow\ --single-quote\ --trailing-comma\ es5
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" Use formatprg when available
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let g:neoformat_try_formatprg = 1
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```
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Each option needs to be escaped with `\`.
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#### Running Prettier manually in Vim
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If you need a little more control over when prettier is run, you can create a
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custom key binding. In this example, `gp` (mnemonic: "get pretty") is used to
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run prettier (with options) in the currently active buffer:
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```vim
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nnoremap gp :silent %!prettier --stdin --trailing-comma all --single-quote<CR>
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```
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### Visual Studio Code
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Can be installed using the extension sidebar. Search for `Prettier - JavaScript formatter`.
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Can also be installed using `ext install prettier-vscode`.
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[Check its repository for configuration and shortcuts](https://github.com/esbenp/prettier-vscode)
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### Visual Studio
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Install the [JavaScript Prettier extension](https://github.com/madskristensen/JavaScriptPrettier).
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### Sublime Text
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Sublime Text support is available through Package Control and
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the [JsPrettier](https://packagecontrol.io/packages/JsPrettier) plug-in.
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### WebStorm
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See the [WebStorm
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guide](https://github.com/jlongster/prettier/tree/master/editors/webstorm/README.md).
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## Language Support
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Prettier attempts to support all JavaScript language features,
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including non-standardized ones. By default it uses the
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[Babylon](https://github.com/babel/babylon) parser with all language
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features enabled, but you can also use the
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[Flow](https://github.com/facebook/flow) parser with the
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`parser` API or `--parser` CLI [option](#options).
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All of JSX and Flow syntax is supported. In fact, the test suite in
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`tests` *is* the entire Flow test suite and they all pass.
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## Related Projects
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- [`eslint-plugin-prettier`](https://github.com/prettier/eslint-plugin-prettier) plugs Prettier into your ESLint workflow
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- [`eslint-config-prettier`](https://github.com/prettier/eslint-config-prettier) turns off all ESLint rules that are unnecessary or might conflict with Prettier
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- [`prettier-eslint`](https://github.com/prettier/prettier-eslint)
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passes `prettier` output to `eslint --fix`
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- [`prettier-standard`](https://github.com/sheerun/prettier-standard)
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uses `prettier` and `prettier-eslint` to format code with standard rules
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- [`prettier-standard-formatter`](https://github.com/dtinth/prettier-standard-formatter)
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passes `prettier` output to `standard --fix`
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- [`prettier-miscellaneous`](https://github.com/arijs/prettier-miscellaneous)
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`prettier` with a few minor extra options
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- [`neutrino-preset-prettier`](https://github.com/SpencerCDixon/neutrino-preset-prettier) allows you to use Prettier as a Neutrino preset
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- [`prettier_d`](https://github.com/josephfrazier/prettier_d.js) runs Prettier as a server to avoid Node.js startup delay
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## Technical Details
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This printer is a fork of
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[recast](https://github.com/benjamn/recast)'s printer with its
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algorithm replaced by the one described by Wadler in "[A prettier
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printer](http://homepages.inf.ed.ac.uk/wadler/papers/prettier/prettier.pdf)".
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There still may be leftover code from recast that needs to be cleaned
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up.
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The basic idea is that the printer takes an AST and returns an
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intermediate representation of the output, and the printer uses that
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to generate a string. The advantage is that the printer can "measure"
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the IR and see if the output is going to fit on a line, and break if
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not.
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This means that most of the logic of printing an AST involves
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generating an abstract representation of the output involving certain
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commands. For example, `concat(["(", line, arg, line ")"])` would
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represent a concatentation of opening parens, an argument, and closing
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parens. But if that doesn't fit on one line, the printer can break
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where `line` is specified.
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More (rough) details can be found in [commands.md](commands.md).
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## Badge
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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)
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```md
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[![styled with prettier](https://img.shields.io/badge/styled_with-prettier-ff69b4.svg)](https://github.com/prettier/prettier)
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```
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## Contributing
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See [CONTRIBUTING.md](CONTRIBUTING.md).
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