React/JSX Style Guide

React/JSX Style Guide

Created
Nov 30, 2021 8:21 AM
Department
Engineering
Category
Code Quality
Technology
ReactJavaScript
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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.

Class vs React.createClass vs stateless

  • If you have an internal state and/or refs, choose between Functional Components or class extends React.Component over React.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>;
      }
    }

    Functional →

    // 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>;
    }

Naming

  • Filename:
    • Use PascalCase for filenames. E.g., ReservationCard.jsx.
    • Now, these are usually for Components, you can stick with camelCase or even small-case / smallcase in some situations.
  • Reference Naming: Use PascalCase for React components and camelCase for their instances.
  • // 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:
    • Let's get some more detail here for styles →
      • The styles, if you're especially using SCSS modules would be the name of the component itself. i.e. Footer.module.scss
      // 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.
    • You can use variants or types ( variants are more preferred ) - you can also structure these out in a separate file and export it as an object. This would streamline the whole process really well
    • // bad
      <MyComponent style="fancy" />
      
      // bad
      <MyComponent className="fancy" />
      
      // good
      <MyComponent variant="fancy" />

Alignment

  • Follow these alignment styles for JSX syntax.
  • // 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.
  • 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.
  • // bad
    <Foo/>
    
    // very bad
    <Foo                 />
    
    // bad
    <Foo
     />
    
    // good
    <Foo />
  • Do not pad JSX curly braces with spaces.
  • // bad
    <Foo bar={ baz } />
    
    // good
    <Foo bar={baz} />

Props

  • Always use camelCase for prop names.
    • There would be some conditions where you might want to send keys or some conditional string with which you can handle some logic. Here you can choose that string to be camelCase or small-case.
    • // bad
      <Foo
        UserName="hello"
        phone_number={12345678}
      />
      
      // good
      <Foo
        userName="hello"
        phoneNumber={12345678}
      />
      
      // For some conditional keys / strings
      
      // good
      <Foo
        origin='about-page'
      />
      
      // good - But keep in mind the above, assuming you have localized project-related strings, the above would be streamlined here.
      <Foo
        origin='aboutPage'
      />

  • Omit the value of the prop when it is explicitly true.
  • // 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".
  • // 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.
  • 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.
  • // 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.
  • 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?)
    • Alternative - Combine the index with a unique identifiable string.
      • Eg. `chapter-${chapterName}-${index}`
      // 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,
    };
  • 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.

// 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.
  • // bad
    <Foo
      ref="myRef"
    />
    
    // good
    <Foo
      ref={(ref) => { this.myRef = ref; }}
    />
    
    // Without callback 
    <Foo
      ref={this.myRef}
    />

Parentheses

  • Wrap JSX tags in parentheses when they span more than one line.
  • // 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.
  • // bad
    <Foo variant="stuff"></Foo>
    
    // good
    <Foo variant="stuff" />
  • If your component has multi-line properties, close its tag on a new line.
  • // 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.
  • 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.
  • // 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
  • 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:
    • displayName
    • propTypes
    • contextTypes
    • childContextTypes
    • mixins
    • statics
    • defaultProps
    • getDefaultProps
    • getInitialState
    • 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.
  • Why? isMounted is an anti-pattern, is not available when using ES6 classes, and is on its way to being officially deprecated.
  • Disclaimer: Inspired by Airbnb JS style guides