A mostly reasonable approach to React and JSX
This style guide is mostly based on the standards that are currently prevalent in JavaScript, although some conventions (i.e async/await or static class fields) may still be included or prohibited on a case-by-case basis. Currently, anything prior to stage 3 is not included nor recommended in this guide.
React.createClass
vs statelessisMounted
react/no-multi-comp
.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
.React.createClass
vs statelessIf 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>;
}
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.
.jsx
extension for React components. eslint: react/jsx-filename-extension
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
andclassName
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" />
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 {
}
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 />}
// good
{someReallyLongConditional
&& anotherLongConditional
&& (
<Foo
superLongParam="bar"
anotherSuperLongParam="baz"
/>
)
}
// good
{someConditional ? (
<Foo />
) : (
<Foo
superLongParam="bar"
anotherSuperLongParam="baz"
/>
)}
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= />
// good
<Foo style= />
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} />
Always use camelCase for prop names, or PascalCase if the prop value is a React component.
// 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
// 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 />
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.
// bad
{todos.map((todo, index) =>
<Todo
{...todo}
key={index}
/>
)}
// good
{todos.map(todo => (
<Todo
{...todo}
key={todo.id}
/>
))}
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,
};
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:
function HOC(WrappedComponent) {
return class Proxy extends React.Component {
Proxy.propTypes = {
text: PropTypes.string,
isLoading: PropTypes.bool
};
render() {
return <WrappedComponent {...this.props} />
}
}
}
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} />
}
Always use ref callbacks. eslint: react/no-string-refs
// bad
<Foo
ref="myRef"
/>
// good
<Foo
ref={(ref) => { this.myRef = ref; }}
/>
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>;
}
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 multiline 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"
/>
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} />;
}
}
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 />);
}
class extends React.Component
:static
methodsconstructor
getChildContext
componentWillMount
componentDidMount
componentWillReceiveProps
shouldComponentUpdate
componentWillUpdate
componentDidUpdate
componentWillUnmount
handleSubmit()
or handleChangeDescription()
onClickSubmit()
or onChangeDescription()
render
like getSelectReason()
or getFooterContent()
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
: eslint: react/sort-comp
displayName
propTypes
contextTypes
childContextTypes
mixins
statics
defaultProps
getDefaultProps
getInitialState
getChildContext
componentWillMount
componentDidMount
componentWillReceiveProps
shouldComponentUpdate
componentWillUpdate
componentDidUpdate
componentWillUnmount
onClickSubmit()
or onChangeDescription()
render
like getSelectReason()
or getFooterContent()
renderNavigation()
or renderProfilePicture()
render
isMounted
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.
This JSX/React style guide is also available in other languages: