# Airbnb React/JSX Style Guide

*A mostly reasonable approach to React and JSX*

## Table of Contents

  1. [Basic Rules](#basic-rules)
  1. [Naming](#naming)
  1. [Declaration](#declaration)
  1. [Alignment](#alignment)
  1. [Quotes](#quotes)
  1. [Spacing](#spacing)
  1. [Props](#props)
  1. [Parentheses](#parentheses)
  1. [Tags](#tags)
  1. [Methods](#methods)
  1. [Ordering](#ordering)
  1. [`isMounted`](#ismounted)

## Basic Rules

  - Only include one React component per file.
  - Always use JSX syntax.
  - Do not use `React.createElement` unless you're initializing the app from a file that is not JSX.

## Class vs React.createClass

  - Use class extends React.Component unless you have a very good reason to use mixins.

  eslint rules: [`react/prefer-es6-class`](https://github.com/yannickcr/eslint-plugin-react/blob/master/docs/rules/prefer-es6-class.md).

  ```javascript
  // bad
  const Listing = React.createClass({
    render() {
      return <div />;
    }
  });

  // good
  class Listing extends React.Component {
    render() {
      return <div />;
    }
  }
  ```

## Naming

  - **Extensions**: Use `.jsx` extension for React components.
  - **Filename**: Use PascalCase for filenames. E.g., `ReservationCard.jsx`.
  - **Reference Naming**: Use PascalCase for React components and camelCase for their instances.

    eslint rules: [`react/jsx-pascal-case`](https://github.com/yannickcr/eslint-plugin-react/blob/master/docs/rules/jsx-pascal-case.md).

    ```javascript
    // bad
    const reservationCard = require('./ReservationCard');

    // good
    const ReservationCard = require('./ReservationCard');

    // bad
    const ReservationItem = <ReservationCard />;

    // good
    const reservationItem = <ReservationCard />;
    ```

    **Component Naming**: Use the filename as the component name. For example, `ReservationCard.jsx` should have a reference name of `ReservationCard`. However, for root components of a directory, use `index.jsx` as the filename and use the directory name as the component name:
    ```javascript
    // bad
    const Footer = require('./Footer/Footer.jsx')

    // bad
    const Footer = require('./Footer/index.jsx')

    // good
    const Footer = require('./Footer')
    ```


## Declaration
  - Do not use displayName for naming components. Instead, name the component by reference.

    ```javascript
    // bad
    export default React.createClass({
      displayName: 'ReservationCard',
      // stuff goes here
    });

    // good
    export default class ReservationCard extends React.Component {
    }
    ```

## Alignment
  - Follow these alignment styles for JSX syntax

  eslint rules: [`react/jsx-closing-bracket-location`](https://github.com/yannickcr/eslint-plugin-react/blob/master/docs/rules/jsx-closing-bracket-location.md).

    ```javascript
    // bad
    <Foo superLongParam="bar"
         anotherSuperLongParam="baz" />

    // good
    <Foo
      superLongParam="bar"
      anotherSuperLongParam="baz"
    />

    // if props fit in one line then keep it on the same line
    <Foo bar="bar" />

    // children get indented normally
    <Foo
      superLongParam="bar"
      anotherSuperLongParam="baz"
    >
      <Spazz />
    </Foo>
    ```

## Quotes
  - Always use double quotes (`"`) for JSX attributes, but single quotes for all other JS.

  > Why? JSX attributes [can't contain escaped quotes](http://eslint.org/docs/rules/jsx-quotes), so double quotes make conjunctions like `"don't"` easier to type.
  > Regular HTML attributes also typically use double quotes instead of single, so JSX attributes mirror this convention.

  eslint rules: [`jsx-quotes`](http://eslint.org/docs/rules/jsx-quotes).

    ```javascript
    // bad
    <Foo bar='bar' />

    // good
    <Foo bar="bar" />

    // bad
    <Foo style={{ left: "20px" }} />

    // good
    <Foo style={{ left: '20px' }} />
    ```

## Spacing
  - Always include a single space in your self-closing tag.
    ```javascript
    // bad
    <Foo/>

    // very bad
    <Foo                 />

    // bad
    <Foo
     />

    // good
    <Foo />
    ```

## Props
  - Always use camelCase for prop names.
    ```javascript
    // bad
    <Foo
      UserName="hello"
      phone_number={12345678}
    />

    // good
    <Foo
      userName="hello"
      phoneNumber={12345678}
    />
    ```

## Parentheses
  - Wrap JSX tags in parentheses when they span more than one line.

  eslint rules: [`react/wrap-multilines`](https://github.com/yannickcr/eslint-plugin-react/blob/master/docs/rules/wrap-multilines.md).

    ```javascript
    /// bad
    render() {
      return <MyComponent className="long body" foo="bar">
               <MyChild />
             </MyComponent>;
    }

    // good
    render() {
      return (
        <MyComponent className="long body" foo="bar">
          <MyChild />
        </MyComponent>
      );
    }

    // good, when single line
    render() {
      const body = <div>hello</div>;
      return <MyComponent>{body}</MyComponent>;
    }
    ```

## Tags
  - Always self-close tags that have no children.

  eslint rules: [`react/self-closing-comp`](https://github.com/yannickcr/eslint-plugin-react/blob/master/docs/rules/self-closing-comp.md).

    ```javascript
    // bad
    <Foo className="stuff"></Foo>

    // good
    <Foo className="stuff" />
    ```

  - If your component has multi-line properties, close its tag on a new line.

  eslint rules: [`react/jsx-closing-bracket-location`](https://github.com/yannickcr/eslint-plugin-react/blob/master/docs/rules/jsx-closing-bracket-location.md).

    ```javascript
    // bad
    <Foo
      bar="bar"
      baz="baz" />

    // good
    <Foo
      bar="bar"
      baz="baz"
    />
    ```

## Methods
  - Do not use underscore prefix for internal methods of a React component.
    ```javascript
    // bad
    React.createClass({
      _onClickSubmit() {
        // do stuff
      }

      // other stuff
    });

    // good
    class extends React.Component {
      onClickSubmit() {
        // do stuff
      }

      // other stuff
    });
    ```

## Ordering

  - Ordering for class extends React.Component:

  1. constructor
  1. optional static methods
  1. getChildContext
  1. componentWillMount
  1. componentDidMount
  1. componentWillReceiveProps
  1. shouldComponentUpdate
  1. componentWillUpdate
  1. componentDidUpdate
  1. componentWillUnmount
  1. *clickHandlers or eventHandlers* like onClickSubmit() or onChangeDescription()
  1. *getter methods for render* like getSelectReason() or getFooterContent()
  1. *Optional render methods* like renderNavigation() or renderProfilePicture()
  1. render

  - How to define propTypes, defaultProps, contextTypes, etc...  

  ```javascript
  import React, { PropTypes } from 'react';

  const propTypes = {
    id: PropTypes.number.isRequired,
    url: PropTypes.string.isRequired,
    text: PropTypes.string,
  };

  const defaultProps = {
    text: 'Hello World',
  };

  class Link extends React.Component {
    static methodsAreOk() {
      return true;
    }

    render() {
      return <a href={this.props.url} data-id={this.props.id}>{this.props.text}</a>
    }
  }

  Link.propTypes = propTypes;
  Link.defaultProps = defaultProps;

  export default Link;
  ```

  - Ordering for React.createClass:

  1. displayName
  1. propTypes
  1. contextTypes
  1. childContextTypes
  1. mixins
  1. statics
  1. defaultProps
  1. getDefaultProps
  1. getInitialState
  1. getChildContext
  1. componentWillMount
  1. componentDidMount
  1. componentWillReceiveProps
  1. shouldComponentUpdate
  1. componentWillUpdate
  1. componentDidUpdate
  1. componentWillUnmount
  1. *clickHandlers or eventHandlers* like onClickSubmit() or onChangeDescription()
  1. *getter methods for render* like getSelectReason() or getFooterContent()
  1. *Optional render methods* like renderNavigation() or renderProfilePicture()
  1. render

  eslint rules: [`react/sort-comp`](https://github.com/yannickcr/eslint-plugin-react/blob/master/docs/rules/sort-comp.md).

## `isMounted`

  [`isMounted` is an anti-pattern][anti-pattern], is not available when using ES6 classes, and is on its way to being officially deprecated. Its use should be avoided.

  [anti-pattern]: https://facebook.github.io/react/blog/2015/12/16/ismounted-antipattern.html

  eslint rules: [`react/no-is-mounted`](https://github.com/yannickcr/eslint-plugin-react/blob/master/docs/rules/no-is-mounted.md).

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