React/JSX Style Guide

Created

Nov 30, 2021 8:21 AM

Department

Engineering

Basic Rules

Only include one React component per file.

However, multiple Stateless, or Pure, Components are allowed 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.

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.

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>;
}

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

React/JSX Style Guide

Basic Rules

Class vs React.createClass vs stateless

Naming

Alignment

Quotes

Spacing

Props

Refs

Parentheses

Tags

Methods

Ordering

isMounted

Class vs `React.createClass` vs stateless

`isMounted`