# babel-plugin-functional-hmr

A [Babel](http://babeljs.io) plugin allows HMR for functional components in React Native.

![](https://raw.githubusercontent.com/bvic23/babel-plugin-functional-hmr/master/demo.gif)

## Limitations

If you try to use [hooks](https://reactjs.org/docs/hooks-intro.html) in your source they won't work (you will get an "Hooks can only be called inside the body of a function component").

## Why?

Hot module reload (HMR) has been [broken for functional components](https://github.com/facebook/react-native/issues/8465) in [React Native](http://www.reactnative.com). 

The "hot loading" message appears, but the changes don't show up.


## Installation

In most cases, you should install `babel-plugin-functional-hmr` as a development dependency (with `--save-dev`).

```sh
npm install --save-dev babel-plugin-functional-hmr
```

or 

```sh
yarn add babel-plugin-functional-hmr -D
```

The transformation plugin is typically used only in development. See the examples below for more details.

## Usage

### Via `.babelrc` (Recommended)

Add the following line to your `.babelrc` file:

Without options:

```json
{
  "plugins": ["functional-hmr"]
}
```

With options:

```json
{
  "plugins": [
    ["functional-hmr"]
  ]
}
```

### Via CLI

```sh
babel --plugins functional-hmr script.js
```

### Via Node API

```js
require("babel-core").transform("code", {
  plugins: ["functional-hmr"]
});
```

### Important Note
From [Issue #5](https://github.com/bvic23/babel-plugin-functional-hmr/issues/5#issuecomment-333309618): *"Editing the `.babelrc` won't actually change the setup, unless you start the packager with `yarn start --reset-cache` to clean the transform cache."*

## Technical details

### Class
The plugin does not transform components defined as classes, such as: 

```js
export default class Button extends Component {
    render() {
        return (
            <TouchableNativeFeedback onPress={this.props.onPress}>
                <Text style={{ color: 'green' }}>
                    {this.props.title}
                </Text>
            </TouchableNativeFeedback>
        );
    }
}
```

### Arrow functions
The plugin transforms arrow expressions **if**:

- it has `JSX` return
- it has only one object parameter or no parameters

It does not transform files located in `node_modules` folder.

From:

```js
const Button = ({ children, onPress }) =>
    <TouchableNativeFeedback onPress={onPress}>
        <Text style={{ color: 'blue' }}>
            {children}
        </Text>
    </TouchableNativeFeedback>;

export default Button;
```

to:

```js
import reactTransform from 'react-transform-hmr';

function wrapComponent(id, Component) {
    const t = reactTransform({
        components: {
            [id]: {
                displayName: id
            }
        },
        locals: [module],
        imports: [require("react")]
    });
    return t(Component, id);
}

class __Button extends require("react").Component {
    render() {
        const children = this.props.children,
              onPress = this.props.onPress;
        return (<TouchableNativeFeedback onPress={onPress}>
        <Text style={{ color: 'blue' }}>
            {children}
        </Text>
    </TouchableNativeFeedback>);
    }

}

const Button = wrapComponent('Button', __Button);
export default Button;
```

Checkout the [tests](https://github.com/bvic23/babel-plugin-functional-hmr/blob/master/lib/__tests__/plugin.test.js) for more examples.


## Sources

- [Babel Plugin Handbook](https://github.com/babel/babel/tree/master/packages/babel-types#babel-types)
- [Babel Types](https://github.com/babel/babel/tree/master/packages/babel-types#babel-types)
- [AST Explorer](https://astexplorer.net)

## License

MIT, see [LICENSE.md](/LICENSE.md) for details.