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.
  • 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.

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 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:

    // 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 .jsx extension for React components. eslint: react/jsx-filename-extension
  • 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';
    
  • 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" />
    
    // bad
    <MyComponent className="fancy" />
    
    // good
    <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>
    
    // bad
    {showButton &&
      <Button />
    }
    
    // bad
    {
      showButton &&
        <Button />
    }
    
    // good
    {showButton && (
      <Button />
    )}
    
    // good
    {showButton && <Button />}
    

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" />
    
  • 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 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.

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

```javascript // bad {todos.map((todo, index) => )}

// good {todos.map(todo => ( ))} ```

  • 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,
    };
    
  • 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.

    Exceptions:

  • HOCs that proxy down props and hoist propTypes

    function HOC(WrappedComponent) {
    return class Proxy extends React.Component {
      Proxy.propTypes = {
        text: PropTypes.string,
        isLoading: PropTypes.bool
      };
    
      render() {
        return <WrappedComponent {...this.props} />
      }
    }
    }
    
  • Spreading 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} />);
    }
    

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

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

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>;
    }
    

Tags

  • Always self-close tags that have no children. eslint: react/self-closing-comp

    // bad
    <Foo variant="stuff"></Foo>
    
    // good
    <Foo variant="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. It is handy when you need to pass additional data to an event handler. Although, make sure they do not massively hurt performance, in particular when passed to custom components that might be PureComponents, because they will trigger a possibly needless rerender every time.

    function ItemList(props) {
      return (
        <ul>
          {props.items.map((item, index) => (
            <Item
              key={item.key}
              onClick={(event) => doSomethingWith(event, 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. Do not use arrow functions in class fields, because it makes them challenging to test and debug, and can negatively impact performance, and because conceptually, class fields are for data, not logic.

    // bad
    class extends React.Component {
      onClickDiv() {
        // do stuff
      }
    
      render() {
        return <div onClick={this.onClickDiv.bind(this)} />;
      }
    }
    
    // very bad
    class extends React.Component {
      onClickDiv = () => {
        // do stuff
      }
    
      render() {
        return <div onClick={this.onClickDiv} />
      }
    }
    
    // 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:
  1. optional static methods
  2. constructor
  3. getChildContext
  4. componentWillMount
  5. componentDidMount
  6. componentWillReceiveProps
  7. shouldComponentUpdate
  8. componentWillUpdate
  9. componentDidUpdate
  10. componentWillUnmount
  11. clickHandlers or eventHandlers like onClickSubmit() or onChangeDescription()
  12. getter methods for render like getSelectReason() or getFooterContent()
  13. optional render methods like renderNavigation() or renderProfilePicture()
  14. 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;
    
  • 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