rofrischmann/elodin

import DocLayout from '../../../../components/DocLayout.js'

export default DocLayout

# JavaScript: Fela

```bash
yarn add --dev @elodin/generator-javascript-fela
```

This generator is used with JavaScript and [Fela](https://fela.js.org).<br />
It renders all styles to [Fela rules](http://fela.js.org/docs/basics/Rules.html) using the [fela-plugin-extend](https://github.com/robinweser/fela/tree/master/packages/fela-plugin-extend) `extend` syntax to render variant conditionals.

## Usage

To use the Fela generator, simply add it to your Elodin configuration and you're ready to go.

```javascript name=elodin.config.js
var { createGenerator } = require('@elodin/generator-javascript-fela')

module.exports = {
  generator: createGenerator(),
}
```

## Configuration

| Option               | Type     | Default                        | Description                                                                                                                                         |
| -------------------- | -------- | ------------------------------ | --------------------------------------------------------------------------------------------------------------------------------------------------- |
| generateStyleName    | Function | _name => name_                 | A function that returns name of the JavaScript function that returns the class name. It takes the style name and returns a string.                  |
| generateFileName     | Function | _module => module + ".elo"_    | A function that represents the JavaScript filename convention. It takes the style and module name. The `.js` extension is applied automatically.    |
| generateVariantName  | Function | _name => uncapitalize(name)_   | A function that generates variant names in our JavaScript files. It represents the property key which we need to pass in order to apply variants.   |
| generateVariantValue | Function | _value => uncapitalize(value)_ | A function that generates variant values in our JavaScript files. It represents the variant value which we need to pass in order to apply variants. |

### Example

```javascript name=elodin.config.js
var { createGenerator } = require('@elodin/generator-javascript-fela')

module.exports = {
  generator: createGenerator({
    // makes variant values uppercase e.g. variant: "PRIMARY"
    generateVariantValue: value => value.toUpperCase(),
  }),
}
```

## Feature Coverage

- Styles
- Primitives
- Variables
- Functions
- Variants
- Conditionals
  - Variants
  - Environment
    - Pseudo Classes
    - Media Queries

---

## Usage Example

```elo name=button.elo
variant Variant {
  Primary
  Secondary
}

style Button {
  paddingLeft: 10
  paddingRight: 10
  minWidth: $minWidth
  [Variant=Primary] {
    backgroundColor: blue
  }
  [Variant=Secondary] {
    backgroundColor: red
  }
}
```

```javascript name=Button.js
import { createRenderer } from 'fela'

import { Button } from './button.elo.js'

// make sure to include the fela-plugin-extend
// it is included in the fela-preset-web
const renderer = createRenderer()

const className = renderer.renderRule(Button, {
  variant: 'primary',
  minWidth: 120,
})

// do something with it
document.getElementById('button').className = className
```