Javascript

React Development Standards

React is a JavaScript library for building user interfaces. We use React at Think Company to build rich, interactive user experiences within web applications. This page contains best practices we follow while writing React code for web applications, and has been adapted from Airbnb’s React/JSX Style Guide.

Basic Rules
Class vs. Functional components
Hooks
Mixins
Naming
Declaration
Alignment
Quotes
Spacing
Props
Refs
Parentheses
Managing State
Tags
Methods
Ordering
Conditional Rendering
isMounted

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, or creating a dynamic component.

Class vs. Functional components

Prefer functional components for new component development. Use hooks to manage internal state. Avoid using React.createClass.

// bad
const Listing = React.createClass({
    render() {
        return <div>{this.state.hello}</div>;
    }
});
 
// better
class Listing extends React.Component {
    render() {
        return <div>{this.state.hello}</div>;
    }
}
 
// best
function Listing() {
    const [hello, setHello] = useState();
    return <div>{hello}</div>;
}

Hooks

Prefer hooks for new components instead of using class-based components with lifecycle methods. For most cases, hooks allow you to achieve the same result as lifecycle methods, using significantly less code that is easier to read.

// Avoid using class-based components with lifecycle methods
 
import React, { Component } from 'react';
 
class Example extends Component {
 
    constructor() {
        this.state = {
            count: 0
        };
    }
 
    render() {
        return (
            <div>
                <p>You clicked {this.state.count} times</p>
                <button onClick={() => this.setState({ count: this.state.count + 1 })}>Click me</button>
            </div>
        );
    }
 
}
 
// Start using functional components with hooks
 
import React, { useState } from 'react';
 
function Example() {
 
  const [count, setCount] = useState(0);
 
  return (
    <div>
      <p>You clicked {count} times</p>
      <button onClick={() => setCount(count + 1)}>
        Click me
      </button>
    </div>
  );
}

Mixins

Do not use mixins.
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.

Naming

Extensions: Always use .jsx extension for React components.
Filename: Use PascalCase for filenames. E.g. 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.

// bad
import Footer from './Footer/FooterContainer';

// bad
import Footer from './Footer/index';

// good
import Footer from './Footer/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: if a native prop is to be passed down to a child DOM element, do not use a modification of the prop name.

/* avoid this… */

function MyComponent({ customClass }) {
    return (
        <p className={customClass}>Hello</p>
    );
}

/* do this instead… */

function MyComponent({ className }) {
    // Note: avoid spreading props "blindly" into a child element, except in HOCs
    // <p {...props}>Hello</p>
    return (
        <p className={className}>Hello</p>
    );
}

Declaration

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 {}

Alignment

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"
    />
)}

Quotes

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={{ left: "20px" }} />

// good
<Foo style={{ left: '20px' }} />
```

Spacing

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} />
```

Props

Use camelCase for prop names. This rule may be more flexible in a .NET environment where keys in a data set are returned in PascalCase.

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

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

Omit the value of the prop when it is explicitly true. eslint: react/jsx-boolean-value
```
// bad
<Foo hidden={true} />

// good
<Foo hidden />
```

Avoid using an array index as key prop, prefer a unique ID. (why?)

// bad
{todos.map((todo, index) =>
<Todo
    {...todo}
    key={index}
/>
)}

// good
{todos.map(todo => (
<Todo
    {...todo}
    key={todo.id}
/>
))}

Typecheck with PropTypes by declaring propTypes above the component declaration. Assign the propTypes to the component below.

// 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

const propTypes = {
    foo: PropTypes.number.isRequired,
    bar: PropTypes.string,
    children: PropTypes.node,
};

function SFC({ foo, bar, children }) {
    return <div>{foo}{bar}{children}</div>;
}

SFC.propTypes = propTypes;

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
const propTypes = {
    foo: PropTypes.number.isRequired,
    bar: PropTypes.string,
    children: PropTypes.node,
};
function SFC({ foo, bar, children }) {
    return (
        <div>
        {foo}
        {bar}
        {children}
        </div>
    );
}

SFC.propTypes = propTypes;

// good
const propTypes = {
    foo: PropTypes.number.isRequired,
    bar: PropTypes.string,
    children: PropTypes.node,
};
const defaultProps = {
    bar: "",
    children: null,
};
function SFC({ foo, bar, children }) {
    return (
        <div>
            {foo}
            {bar}
            {children}
        </div>
    );
}

SFC.propTypes = propTypes;
SFC.defaultProps = defaultProps;

Deepcheck props with propTypes where applicable.

Why? Deepchecking allows React to to better validate props and provides even more clarity around what props the component is expecting.

// bad
const propTypes = {
    foo: PropTypes.array.isRequired
};
// good
const propTypes = {
    foo: PropTypes.arrayOf(PropTypes.shape({
        id: PropTypes.string.isRequired,
        name: PropTypes.string.isRequired
    })).isRequired,
};

Use spread props sparingly.

Why? Otherwise you’re more likely to pass unnecessary props down to components.

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, or the useRef hook. eslint: react/no-string-refs

// bad
<Foo ref="myRef" />

// good
<Foo
    ref={(ref) => { this.myRef = ref; }}
/>

// good
const myRef = useRef();
<Foo ref={myRef} />

Parentheses

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>;
}

Managing State

For managing state of a single component that does not need to be shared outside of the component, use the useState hook.
For managing state within a component tree with more than two levels, use Context.
For managing state of an application that will be shared by all components, use Redux with Redux Toolkit (RTK).

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, 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={() => doSomethingWith(item.name, index)}
        />
    ))}
    </ul>
);
}
```

Bind event handlers for the render method using an arrow function in the class property. This approach requires transform-class-properties or enable stage-2 in Babel. eslint: react/jsx-no-bind

Why? Other methods of binding have minor performance, readability, and maintainability concerns. For a more in depth explanation of options and reasons, see React Binding Patterns.

// bad
class extends React.Component {
    onClickDiv() {
        // do stuff
    }

    render() {
        
        return <div onClick={this.onClickDiv.bind(this)} />;
    }
}

// bad
class extends React.Component {
    constructor(props) {
        super(props);
        this.onClickDiv = this.onClickDiv.bind(this);
    }

    onClickDiv() {
        // do stuff
    }

    render() {
        return <div onClick={this.onClickDiv} />;
    }
}

// good
class extends React.Component {
    constructor(props) {
        super(props);
    }

    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 #490for a more in-depth discussion.
```
// bad
React.createClass({
    _onClickSubmit() {
        // do stuff
    }

    // other stuff
});

// good
class MyComponent 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 />);
}

Ordering

The recommended 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;

Conditional Rendering

Conditionals in markup are ok as long as they are simplified and easy to understand.
Avoid adding methods that return markup that should be a component.
Do not use multiple nested ternaries. Break into multiple components instead.
When in doubt, break down into more components if things are getting complicated.
“If the logic is too complex to be appropriate inline, then it belongs in a separate component.” -> https://github.com/airbnb/javascript/issues/520

`isMounted`

Do not use 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.

Think Company Front-End Web Development Standards