Created
Nov 30, 2021 8:21 AM
Department
Engineering
Category
Code Quality
Technology
ReactJavaScript
Tags
Date
URL
- Basic Rules
- Class vs React.createClass vs stateless
- Naming
- Alignment
- Quotes
- Spacing
- Props
- Refs
- Parentheses
- Tags
- Methods
- Ordering
- isMounted
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
orclass extends React.Component
overReact.
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.
- Component Naming: Use the filename as the component name. For example,
ReservationCard.jsx
should have a reference name ofReservationCard
. However, for root components of a directory, useindex.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
- 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 componentwithFoo()
, when passed a componentBar
should produce a component with adisplayName
ofwithFoo(Bar)
. - Props Naming: Avoid using DOM component prop names for different purposes.
- 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
import reservationCard from "./ReservationCard";
// good
import ReservationCard from "./ReservationCard";
// bad
const ReservationItem = <ReservationCard />;
// good
const reservationItem = <ReservationCard />;
// bad
import Footer from "./Footer/Footer";
// bad
import Footer from "./Footer/index";
// good
import Footer from "./Footer";
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;
}
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" />
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.
- Do not pad JSX curly braces with spaces.
// bad
<Foo/>
// very bad
<Foo />
// bad
<Foo
/>
// good
<Foo />
// 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.
- Omit the value of the prop when it is explicitly
true
. - Always include an
alt
prop on<img>
tags. If the image is presentational,alt
can be an empty string or the<img>
must haverole="presentation"
. - Do not use words like “image”, “photo”, or “picture” in
<img>
alt
props. - Use only valid, non-abstract ARIA roles.
- Do not use
accessKey
on elements. - 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}`
- Always define explicit defaultProps for all non-required props.
- 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.
// 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'
/>
// bad
<Foo
hidden={true}
/>
// good
<Foo
hidden
/>
// good
<Foo hidden />
// 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" />
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" />
// bad - not an ARIA role
<div role="datepicker" />
// bad - abstract ARIA role
<div role="range" />
// good
<div role="button" />
Why? Inconsistencies between keyboard shortcuts and keyboard commands used by people using screenreaders and keyboards complicate accessibility.// bad <div accessKey="h" /> // good <div />
// 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,
};
Exceptions:
- HOCs that proxy down props and hoist propTypes
- Spreading objects with known, explicit props. This can be particularly useful when testing React components with Mocha’s beforeEach construct.
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.
// 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.
- If your component has multi-line properties, close its tag on a new line.
// bad
<Foo variant="stuff"></Foo>
// good
<Foo variant="stuff" />
// bad
<Foo
bar="bar"
baz="baz" />
// good
<Foo
bar="bar"
baz="baz"
/>
Methods
- Use arrow functions to close over local variables.
- Bind event handlers for the render method in the constructor.
- Do not use underscore prefix for internal methods of a React component.
- Be sure to return a value in your
render
methods.
function ItemList(props) {
return (
<ul>
{props.items.map((item, index) => (
<Item
key={item.key}
onClick={() => doSomethingWith(item.name, index)}
/>
))}
</ul>
);
}
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} />;
}
}
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
}
// 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()
oronChangeDescription()
- getter methods for
render
likegetSelectReason()
orgetFooterContent()
- optional render methods like
renderNavigation()
orrenderProfilePicture()
render
- How to define
propTypes
,defaultProps
,contextTypes
, etc… - 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()
oronChangeDescription()
- getter methods for
render
likegetSelectReason()
orgetFooterContent()
- optional render methods like
renderNavigation()
orrenderProfilePicture()
render
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;
isMounted
- Do not use
isMounted
. - Disclaimer: Inspired by Airbnb JS style guides
Why? isMounted is an anti-pattern, is not available when using ES6 classes, and is on its way to being officially deprecated.