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Airbnb React/JSX Style Guide

A mostly reasonable approach to React and JSX

This style guide is mostly based on the standards that are currently prevalent in JavaScript, although some conventions (i.e async/await or static class fields) may still be included or prohibited on a case-by-case basis. Currently, anything prior to stage 3 is not included nor recommended in this guide.

Basic Rules
Class vs React.createClass vs stateless
Mixins
Naming
Declaration
Alignment
Quotes
Spacing
Props
Refs
Parentheses
Tags
Methods
Ordering
isMounted

Basic Rules

Always use JSX syntax.
Do not use React.createElement unless you’re initializing the app from a file that is not JSX.
react/forbid-prop-types will allow arrays and objects only if it is explicitly noted what array and object contains, using arrayOf, objectOf, or shape. TODO: add this

Class vs stateless

If you have internal state and/or refs, prefer class extends React.Component over React.createClass. eslint: react/prefer-es6-class react/prefer-stateless-function TODO: When to use component vs functinal vs pure (no more createClass)

// bad
const Listing = React.createClass({
  // ...
  render() {
    return <div>{this.state.hello}</div>;
  }
});

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

And if you don’t have state or refs, prefer normal functions (not arrow functions) over classes: TODO: pull this into own section

// bad
class Listing extends React.Component {
  render() {
    return <div>{this.props.hello}</div>;
  }
}

// good
const Listing = ({ hello }) => (
  <div>{hello}</div>
);

// good
function Listing({ hello }) {
  return <div>{hello}</div>;
}

Mixins

Do not use mixins.

Why? Mixins introduce implicit dependencies, cause name clashes, and cause snowballing complexity. Most use cases for mixins can be accomplished in better ways via components, higher-order components, or utility modules.

Naming

Filename: Use PascalCase for filenames. E.g., ReservationCard.js.

Reference Naming: TODO: If we do this. Use PascalCase for React components and camelCase for their instances. eslint: react/jsx-pascal-case

// bad
import reservationCard from './ReservationCard';

// good
import ReservationCard from './ReservationCard';

// bad
const ReservationItem = <ReservationCard />;

// good
const reservationItem = <ReservationCard />;

Component Naming: Use the filename as the component name. For example, ReservationCard.js should have a reference name of ReservationCard. However, for root components of a directory, use index.js as the filename and use the directory name as the component name:
```
// bad
import Footer from './Footer/Footer';

// bad
import Footer from './Footer/index';

// good
import Footer from './Footer';
```
Props Naming: Avoid using DOM component prop names for different purposes.

Why? People expect props like style and className to mean one specific thing. Varying this API for a subset of your app makes the code less readable and less maintainable, and may cause bugs.
```
// bad
<MyComponent style="fancy" />

// good
<MyComponent variant="fancy" />
```

Alignment

Follow these alignment styles for JSX syntax. eslint: react/jsx-closing-bracket-location react/jsx-closing-tag-location

// 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"
>
  <Quux />
</Foo>

// bad
{showButton &&
  <Button />
}

// bad
{
  showButton &&
    <Button />
}

// good
{showButton && (
  <Button>
    <span>Hi</span>
  </Button>
)}

// good
{showButton && <Button />}

Quotes

Always use double quotes (") for JSX attributes, but single quotes (') for all other JS. eslint: jsx-quotes TODO: We do the opposite, no reason but this is what we use

Why? Regular HTML attributes also typically use double quotes instead of single, so JSX attributes mirror this convention.
```
// 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. eslint: no-multi-spaces, react/jsx-tag-spacing

// bad
<Foo/>

// very bad
<Foo                 />

// bad
<Foo
 />

// good
<Foo />

Do not pad JSX curly braces with spaces. eslint: react/jsx-curly-spacing TODO: prettier fixes, but we don't enforce
```
// bad
<Foo bar={ baz } />

// good
<Foo bar={baz} />
```

Props

Always use camelCase for prop names.

// bad
<Foo
  UserName="hello"
  phone_number={1234567890}
/>

// good
<Foo
  userName="hello"
  phoneNumber={1234567890}
/>

Omit the value of the prop when it is explicitly true. eslint: react/jsx-boolean-value

// bad
<Foo
  hidden={true}
/>

// good
<Foo
  hidden
/>

// good
<Foo hidden />

Always include an alt prop on <img> tags. If the image is presentational, alt can be an empty string or the <img> must have role="presentation". eslint: jsx-a11y/alt-text

// bad
<img src="hello.jpg" />

// good
<img src="hello.jpg" alt="Me waving hello" />

// good
<img src="hello.jpg" alt="" />

// good
<img src="hello.jpg" role="presentation" />

Do not use words like "image", "photo", or "picture" in <img> alt props. eslint: jsx-a11y/img-redundant-alt

Why? Screenreaders already announce img elements as images, so there is no need to include this information in the alt text.
```
// bad
<img src="hello.jpg" alt="Picture of me waving hello" />

// good
<img src="hello.jpg" alt="Me waving hello" />
```

Use only valid, non-abstract ARIA roles. eslint: jsx-a11y/aria-role

// bad - not an ARIA role
<div role="datepicker" />

// bad - abstract ARIA role
<div role="range" />

// good
<div role="button" />

Do not use accessKey on elements. (eslint rule not enforced) eslint: jsx-a11y/no-access-key

Why? Inconsistencies between keyboard shortcuts and keyboard commands used by people using screenreaders and keyboards complicate accessibility.

// bad
<div accessKey="h" />

// good
<div />

Avoid using an array index as key prop, prefer a stable ID. eslint: react/no-array-index-key

Why? Not using a stable ID is an anti-pattern because it can negatively impact performance and cause issues with component state. TODO: Determine better patterns

We don’t recommend using indexes for keys if the order of items may change.

// bad
{todos.map((todo, index) =>
  <Todo
    {...todo}
    key={index}
  />
)}

// good
{todos.map(todo => (
  <Todo
    {...todo}
    key={todo.id}
  />
))}

Always define explicit defaultProps for all non-required props.

Why? propTypes are a form of documentation, and providing defaultProps means the reader of your code doesn’t have to assume as much. In addition, it can mean that your code can omit certain type checks.

// bad
function SFC({ foo, bar, children }) {
  return <div>{foo}{bar}{children}</div>;
}
SFC.propTypes = {
  foo: PropTypes.number.isRequired,
  bar: PropTypes.string,
  children: PropTypes.node,
};

// good
function SFC({ foo, bar, children }) {
  return <div>{foo}{bar}{children}</div>;
}
SFC.propTypes = {
  foo: PropTypes.number.isRequired,
  bar: PropTypes.string,
  children: PropTypes.node,
};
SFC.defaultProps = {
  bar: '',
  children: null,
};

Don't pass unnecessary props down to components.

Why? You may pass props the component doesn't care about that may cause it to re-render.

You may spread objects with known, explicit props. This can be particularly useful when testing React components with Mocha’s beforeEach construct.

export default function Foo {
  const props = {
    text: '',
    isPublished: false
  }

  return (<div {...props} />);
}

Refs

If you must use ref callbacks. eslint: react/no-string-refs TODO: confirm current React ref preferences, wrap it in a ref wrapper
```
// bad
<Foo
  ref="myRef"
/>

// good
<Foo
  ref={(ref) => { this.myRef = ref; }}
/>
```

Parentheses

Wrap JSX tags in parentheses when they span more than one line. eslint: react/jsx-wrap-multilines

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

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

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

Methods

Bind event handlers for the render method in the constructor. eslint: react/jsx-no-bind TODO: Good Arrow function example

Why? A bind call in the render path creates a brand new function on every single render.

// bad
class extends React.Component {
  onClickDiv() {
    // do stuff
  }

  render() {
    return <div onClick={this.onClickDiv.bind(this)} />;
  }
}

// bad
class extends React.Component {
  constructor(props) {
    super(props);

    this.onClickDiv = this.onClickDiv.bind(this);
  }

  onClickDiv() {
    // do stuff
  }

  render() {
    return <div onClick={this.onClickDiv} />;
  }
}

Be sure to return a value in your render methods. eslint: react/require-render-return

// bad
render() {
  (<div />);
}

// good (TODO: make better, not empty div)
render() {
  return (<div />);
}

Ordering

Simplify: Render bottom, constructor top, lifecycle middle etc, etc.
Ordering for class extends React.Component:

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

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

import React from 'react';
import PropTypes from 'prop-types';

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;

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README.md

Airbnb React/JSX Style Guide

Table of Contents

Basic Rules

Class vs stateless

Mixins

Naming

Alignment

Quotes

Spacing

Props

Refs

Parentheses

Tags

Methods

Ordering

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react

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parent directory

README.md

Airbnb React/JSX Style Guide

Table of Contents

Basic Rules

Class vs stateless

Mixins

Naming

Alignment

Quotes

Spacing

Props

Refs

Parentheses

Tags

Methods

Ordering