react

Quri React/JSX Style Guide

A mostly reasonable approach to React and JSX

Table of Contents

1. Basic Rules
2. Class vs React.createClass vs stateless
3. Mixins
4. Naming
5. Declaration
6. Alignment
7. Quotes
8. Spacing
9. Props
10. Refs
11. Parentheses
12. Tags
13. Methods
14. Ordering
15. isMounted
16. Using ES7 Features

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

• 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

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

  // bad
  class Listing extends React.Component {
    render() {
      return <div>{this.props.hello}</div>;
    }
  }
  
  // bad (relying on function name inference is discouraged)
  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

• Extensions: Use .js extension for React components.

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

• 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';

• Higher-order Component Naming: Use a composite of the higher-order component's name and the passed-in component's name as the displayName on the generated component. For example, the higher-order component withFoo(), when passed a component Bar should produce a component with a displayName of withFoo(Bar).

  Why? A component's displayName may be used by developer tools or in error messages, and having a value that clearly expresses this relationship helps people understand what is happening.

  // bad
  export default function withFoo(WrappedComponent) {
    return function WithFoo(props) {
      return <WrappedComponent {...props} foo />;
    }
  }
  
  // good
  export default function withFoo(WrappedComponent) {
    function WithFoo(props) {
      return <WrappedComponent {...props} foo />;
    }
  
    const wrappedComponentName = WrappedComponent.displayName
      || WrappedComponent.name
      || 'Component';
  
    WithFoo.displayName = `withFoo(${wrappedComponentName})`;
    return WithFoo;
  }

• 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" />

• Selector Naming: Selector function names should be appended with Selector. Prepending with get is oftentimes redundant and unnecessary:

  // bad
  const getTotal = createSelector(
    [state => state.values.value1, state => state.values.value2],
    (value1, value2) => value1 + value2
  )
  
  // bad
  const getTotalSelector = createSelector(
    [state => state.values.value1, state => state.values.value2],
    (value1, value2) => value1 + value2
  )
  
  // good
  const totalSelector = createSelector(
    [state => state.values.value1, state => state.values.value2],
    (value1, value2) => value1 + value2
  )
  

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 Component {
  }

Alignment

• Follow these alignment styles for JSX syntax. eslint: react/jsx-closing-bracket-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 (").

  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-space-before-closing

  // 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
  />

• 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/img-has-alt

  // 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: 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 unique ID. (why?)

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

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 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: react/self-closing-comp

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

• If your component has multi-line properties, close its tag on a new line. eslint: react/jsx-closing-bracket-location

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

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 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 Component:

1. optional static methods
2. mixins
3. displayName
4. propTypes
5. paginationId
6. headers
7. scopesDef
8. contextTypes
9. childContextTypes
10. optional static methods
11. defaultProps
12. constructor
13. getDefaultProps
14. getInitialState
15. state
16. constructor
17. getChildContext
18. componentWillMount
19. componentDidMount
20. componentWillReceiveProps
21. shouldComponentUpdate
22. componentWillUpdate
23. componentDidUpdate
24. componentWillUnmount
25. clickHandlers or eventHandlers like onClickSubmit() or onChangeDescription()
26. getter methods for render like getSelectReason() or getFooterContent()
27. optional render methods like renderNavigation() or renderProfilePicture()
28. render

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

  Use ES7 static class properties : documentation / babel support

  import React, { PropTypes } from 'react';
  
  export default class Link extends React.Component {
    static propTypes = {
      id: PropTypes.number.isRequired,
      url: PropTypes.string.isRequired,
      text: PropTypes.string,
    };
  
    static defaultProps = {
      text: 'Hello World',
    };
  
  
    static methodsAreOk() {
      return true;
    }
  
    render() {
      return <a href={this.props.url} data-id={this.props.id}>{this.props.text}</a>
    }
  }

• Ordering for React.createClass: eslint: react/sort-comp

1. displayName
2. propTypes
3. contextTypes
4. childContextTypes
5. mixins
6. statics
7. defaultProps
8. getDefaultProps
9. getInitialState
10. getChildContext
11. componentWillMount
12. componentDidMount
13. componentWillReceiveProps
14. shouldComponentUpdate
15. componentWillUpdate
16. componentDidUpdate
17. componentWillUnmount
18. clickHandlers or eventHandlers like onClickSubmit() or onChangeDescription()
19. getter methods for render like getSelectReason() or getFooterContent()
20. optional render methods like renderNavigation() or renderProfilePicture()
21. 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.

Translation

This JSX/React style guide is also available in other languages:

• Chinese (Simplified): JasonBoy/javascript
• Polish: pietraszekl/javascript
• Korean: apple77y/javascript
• Portuguese: ronal2do/javascript
• Japanese: mitsuruog/javascript-style-guide
• Español: agrcrobles/javascript
• Ukrainian: ivanzusko/javascript

⬆ back to top

Using ES7 features

We use a few useful features that were not included in ES2015 final specification. Thanks to Babel and its plugin system we can use them today:

• transform-object-rest-spread
• syntax-trailing-function-commas
• transform-class-properties

The one feature to highlight is transform-class-properties. With the ES6 class syntax, React component functions are not auto-bound to this (see explanation). Class properties combined with arrow functions allows us to bind class member to this without having to bind every single function in the constructor. They also let us put our propTypes and defaultProps back into the class declaration.

  // bad
  class Card extends Component {

    constructor(props) {
      super(props);
      this.handleChange = this.handleChange.bind(this);
      this.handleClick = this.handleClick.bind(this);
    }

    handleChange() {
      this.props.onChange({do: "something"});
    }

    handleClick() {
    	this.props.onClick({click: "somewhere"});
    }

    render() {
      return <span onClick={this.handleClick} onChange={this.handleChange}>I am a Card !</span>;
    }

  }

  Card.propTypes = {
    onChange: PropType.func.isRequired,
    onClick: PropTypes.func.isRequired
  }

  // Good
  class Card extends Component {

    static propTypes = {
      onChange: PropType.func.isRequired,
      onClick: PropTypes.func.isRequired
    }

    handleChange = () => {
      this.props.onChange({do: "something"});
    }

    handleClick = () => {
    	this.props.onClick({click: "somewhere"});
    }

    render() {
      return <span onClick={this.handleClick} onChange={this.handleChange}>I am a Card !</span>;
    }

  }