A mostly reasonable approach to React and JSX

1. Basic Rules
2. Class vs React.createClass vs stateless
3. Naming
4. Declaration
5. Alignment
6. Quotes
7. Spacing
8. Props
9. Parentheses
10. Tags
11. Methods
12. Ordering
13. isMounted

• Only include one React component per file.
  • However, multiple Stateless, or Pure, Components are allowed per file. eslint rule: react/no-multi-comp.
• Always use JSX syntax.
• Do not use React.createElement unless you're initializing the app from a file that is not JSX.

• If you have internal state and/or refs, prefer class extends React.Component over React.createClass unless you have a very good reason to use mixins.

eslint rules: react/prefer-es6-class.

```javascript
// 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 functions over classes:

```javascript

// bad
class Listing extends React.Component {
  render() {
    return <div>{this.props.hello}</div>;
  }
}

// good
function Listing({ hello }) {
  return <div>{hello}</div>;
}
```

• Extensions: 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 rules: react/jsx-pascal-case.

```javascript
// 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';

• 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 rules: react/jsx-closing-bracket-location.

```javascript
// 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"
>
  <Spazz />
</Foo>
```

• Always use double quotes (") for JSX attributes, but single quotes for all other JS.

Why? JSX attributes can't contain escaped quotes, so double quotes make conjunctions like "don't" easier to type. Regular HTML attributes also typically use double quotes instead of single, so JSX attributes mirror this convention.

eslint rules: jsx-quotes.

```javascript
// bad
<Foo bar='bar' />

// good
<Foo bar="bar" />

// bad
<Foo style={{ left: "20px" }} />

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

• Always include a single space in your self-closing tag.

  // bad
  <Foo/>
  
  // very bad
  <Foo                 />
  
  // bad
  <Foo
   />
  
  // good
  <Foo />

• Always use camelCase for prop names.

  // 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 rules: react/jsx-boolean-value.

```javascript
// bad
<Foo
  hidden={true}
/>

// good
<Foo
  hidden
/>
```

• Wrap JSX tags in parentheses when they span more than one line.

eslint rules: react/wrap-multilines.

```javascript
// bad
render() {
  return <MyComponent className="long body" foo="bar">
           <MyChild />
         </MyComponent>;
}

// good
render() {
  return (
    <MyComponent className="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 rules: react/self-closing-comp.

```javascript
// bad
<Foo className="stuff"></Foo>

// good
<Foo className="stuff" />
```

• If your component has multi-line properties, close its tag on a new line.

eslint rules: react/jsx-closing-bracket-location.

```javascript
// bad
<Foo
  bar="bar"
  baz="baz" />

// good
<Foo
  bar="bar"
  baz="baz"
/>
```

• 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.

eslint rules: react/jsx-no-bind.

```javascript
// 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.

  // bad
  React.createClass({
    _onClickSubmit() {
      // do stuff
    },
  
    // other stuff
  });
  
  // good
  class extends React.Component {
    onClickSubmit() {
      // do stuff
    }
  
    // other stuff
  }

• Ordering for class extends React.Component:

1. constructor
2. optional static methods
3. getChildContext
4. componentWillMount
5. componentDidMount
6. componentWillReceiveProps
7. shouldComponentUpdate
8. componentWillUpdate
9. componentDidUpdate
10. componentWillUnmount
11. clickHandlers or eventHandlers like onClickSubmit() or onChangeDescription()
12. getter methods for render like getSelectReason() or getFooterContent()
13. Optional render methods like renderNavigation() or renderProfilePicture()
14. render

• How to define propTypes, defaultProps, contextTypes, etc...

  import React, { PropTypes } from 'react';
  
  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:

1. displayName
2. propTypes
3. contextTypes
4. childContextTypes
5. mixins
6. statics
7. defaultProps
8. getDefaultProps
9. getInitialState
10. getChildContext
11. componentWillMount
12. componentDidMount
13. componentWillReceiveProps
14. shouldComponentUpdate
15. componentWillUpdate
16. componentDidUpdate
17. componentWillUnmount
18. clickHandlers or eventHandlers like onClickSubmit() or onChangeDescription()
19. getter methods for render like getSelectReason() or getFooterContent()
20. Optional render methods like renderNavigation() or renderProfilePicture()
21. render

eslint rules: react/sort-comp.

• 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.

eslint rules: react/no-is-mounted.

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