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Airbnb React/JSX Style Guide

A mostly reasonable approach to React and JSX

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

Basic Rules

Only include one React component per file.
- However, multiple Stateless, or Pure, Components are allowed per file. eslint: react/no-multi-comp.
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` vs stateless

Prefer classes inheriting from React.Component regardless if the component is stateless or not. This is because classes are easy to configure, i.e. adding or removing methods, whenever needed.

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

// bad (relying on function name inference is discouraged)
const Listing = ({ hello }) => (
  <div>{hello}</div>
);

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

Do not use HOCs.

HOCs are hard to maintain and unintuitive. Resort on using common components for similar functionality.

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: 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.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:
```
// 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.

Except for className, which is a passthrough and appended on the components' own classes, people expect props like style 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 className="fancy" />

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

Declaration

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

// 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: 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>

Quotes

Always use double quotes (") for JSX attributes, but single quotes (') for all other JS. eslint: jsx-quotes

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

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

Props

Always use camelCase for prop names.

// bad
<Foo
  UserName="hello"
  phone_number={12345678}
/>

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

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" />
```
Avoid using an array index as key prop, prefer a unique ID. (why?)

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

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

Use spread props sparingly.

Why? Otherwise you're more likely to pass unnecessary props down to components. And for React v15.6.1 and older, you could pass invalid HTML attributes to the DOM.

Notes for use: Filter out unnecessary props when possible. Also, use prop-types-exact to help prevent bugs.

//good
render() {
  const { irrelevantProp, ...relevantProps  } = this.props;
  return <WrappedComponent {...relevantProps} />
}

//bad
render() {
  const { irrelevantProp, ...relevantProps  } = this.props;
  return <WrappedComponent {...this.props} />
}

Refs

Always use ref callbacks. eslint: react/no-string-refs

// 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

Use arrow functions to close over local variables.

function ItemList(props) {
  return (
    <ul>
      {props.items.map((item, index) => (
        <Item
          key={item.key}
          onClick={() => doSomethingWith(item.name, index)}
        />
      ))}
    </ul>
  );
}

Bind event handlers for the render method in the constructor. eslint: react/jsx-no-bind

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)} />;
  }
}

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

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

  onClickDiv() {
    // do stuff
  }

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

Do not use underscore prefix for internal methods of a React component.

Why? Underscore prefixes are sometimes used as a convention in other languages to denote privacy. But, unlike those languages, there is no native support for privacy in JavaScript, everything is public. Regardless of your intentions, adding underscore prefixes to your properties does not actually make them private, and any property (underscore-prefixed or not) should be treated as being public. See issues #1024, and #490 for a more in-depth discussion.
```
// bad
React.createClass({
  _onClickSubmit() {
    // do stuff
  },

  // other stuff
});

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

  // other stuff
}
```

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

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

// good
render() {
  return (<div />);
}

Ordering

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

`isMounted`

Do not use isMounted. eslint: react/no-is-mounted

Why? isMounted is an anti-pattern, is not available when using ES6 classes, and is on its way to being officially deprecated.

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README.md

Airbnb React/JSX Style Guide

Table of Contents

Basic Rules

Class vs `React.createClass` vs stateless

Mixins

Naming

Declaration

Alignment

Quotes

Spacing

Props

Refs

Parentheses

Tags

Methods

Ordering

`isMounted`

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parent directory

README.md

Airbnb React/JSX Style Guide

Table of Contents

Basic Rules

Class vs React.createClass vs stateless

Mixins

Naming

Declaration

Alignment

Quotes

Spacing

Props

Refs

Parentheses

Tags

Methods

Ordering

isMounted

Class vs `React.createClass` vs stateless

`isMounted`