React Style Guide
Tags: react, codequality, javascript, beginners
Published: 2021-04-29 08:54:01

# React Style Guide (2021)
src: the original post: https://github.com/airbnb/javascript/tree/master/react

>I wanted to create this post to mark back what's important when someone is just starting out with React. Therefore, I would like to receive comments from everyone.

## Basic Rules
- Only include one React component per file.
- Always use JSX syntax.

## Naming

- **List itemExtensions**: Use `.jsx` extension for React components. eslint: [react/jsx-filename-extension](https://github.com/yannickcr/eslint-plugin-react/blob/master/docs/rules/jsx-filename-extension.md)
- **Filename**: Use `PascalCase` for filenames. E.g., **ReservationCard**.jsx.
- **Reference Naming**: Use `PascalCase` for React components and `camelCase` for  their instances.

```javascript
// 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:

```javascript
// 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.

    ```javascript
    // 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;
    }
    ```
 
## 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 function ReservationCard(props) {
		return ()
	}
    ```

## Alignment

  - Follow these alignment styles for JSX syntax. eslint: [`react/jsx-closing-bracket-location`](https://github.com/yannickcr/eslint-plugin-react/blob/master/docs/rules/jsx-closing-bracket-location.md) [`react/jsx-closing-tag-location`](https://github.com/yannickcr/eslint-plugin-react/blob/master/docs/rules/jsx-closing-tag-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"
    >
      <Quux />
    </Foo>

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

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

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

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

    // good
    {someReallyLongConditional
      && anotherLongConditional
      && (
        <Foo
          superLongParam="bar"
          anotherSuperLongParam="baz"
        />
      )
    }

    // good
    {someConditional ? (
      <Foo />
    ) : (
      <Foo
        superLongParam="bar"
        anotherSuperLongParam="baz"
      />
    )}
    ```

## Props

  - Always use **camelCase** for prop names, or **PascalCase** if the prop value is a React component.

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

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

  - Omit the value of the prop when it is explicitly `true`. eslint: [`react/jsx-boolean-value`](https://github.com/yannickcr/eslint-plugin-react/blob/master/docs/rules/jsx-boolean-value.md)

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

    // good
    <Foo
      hidden
    />

    // very good
    <Foo hidden />
    ```
 
  - Avoid using an array index as `key` prop, prefer a stable ID. eslint: [`react/no-array-index-key`](https://github.com/yannickcr/eslint-plugin-react/blob/master/docs/rules/no-array-index-key.md)

> Why? Not using a stable ID [is an anti-pattern](https://medium.com/@robinpokorny/index-as-a-key-is-an-anti-pattern-e0349aece318) 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) =>
    <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.

  ```javascript
  // 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](https://reactjs.org/blog/2017/09/08/dom-attributes-in-react-16.html).

  Exceptions:

  - HOCs that proxy down props and hoist propTypes

  ```javascript
  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.

  ```javascript
  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](https://www.npmjs.com/package/prop-types-exact) to help prevent bugs.

  ```javascript
  // 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`](https://github.com/yannickcr/eslint-plugin-react/blob/master/docs/rules/no-string-refs.md)

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

    ```javascript
    // 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. It is handy when you need to pass additional data to an event handler. Although, make sure they [do not massively hurt performance](https://www.bignerdranch.com/blog/choosing-the-best-approach-for-react-event-handlers/), in particular when passed to custom components that might be PureComponents, because they will trigger a possibly needless rerender every time.

    ```javascript
    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`](https://github.com/yannickcr/eslint-plugin-react/blob/master/docs/rules/jsx-no-bind.md)

    > 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](https://medium.com/@charpeni/arrow-functions-in-class-properties-might-not-be-as-great-as-we-think-3b3551c440b1), and because conceptually, class fields are for data, not logic.

    ```javascript
    // 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](https://github.com/airbnb/javascript/issues/1024), and [#490](https://github.com/airbnb/javascript/issues/490) for a more in-depth discussion.

    ```javascript
    // 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`](https://github.com/yannickcr/eslint-plugin-react/blob/master/docs/rules/require-render-return.md)

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

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