# Advanced Usage

## Custom MDX components

MDX Deck includes default components for MDX, but to provide custom components to the [MDXProvider][], add a `components` object to the `theme`.

```js
// example theme
import Heading from './Heading'

export default {
  components: {
    h1: Heading,
  },
}
```

See the [MDX][] docs for more or take a look
at the [default set of components](../packages/components/src/mdx-components.js) as a reference.

## Custom Provider component

A custom Provider component is useful for adding custom context providers in React or adding persistent UI elements to the entire deck.

To define a custom Provider component, you'll need to import it into your custom theme and set it using the key `Provider` like shown below:

```js
// example theme.js
import Provider from './Provider'

export default {
  font: 'Georgia, serif',
  Provider,
}
```

A custom Provider component will receive the application's state as props,
which can be used to show custom page numbers or add other elements to the UI.

#### Props

- `slides`: (array) the components for each slide
- `index`: (number) the current slide index
- `mode`: (string) the current mode (one of `'normal'`, `'presenter'`, or `'overview'`)
- `step`: (number) the current visible step in an Appear or Step component
- Each slide includes a `meta` object with a `notes` field when the Notes component is used within a slide

#### Example

The example below will display the current slide out of the total amount of slides.

```js
import React from 'react'
import { css } from '@emotion/core'

function AtTheBottomCenter ({ children }) {
  const css = {
    position: 'absolute',
    left: 0,
    right: 0,
    bottom: 0,
    color: #ffffff;
    textAlign: 'center',
  }

  return <div css={ css }>
    { children }
  </div>
}

export function Provider ({ children, ...props }) {
  return <>
    { children }
    <AtTheBottomCenter>{ props.index }/{ props.slides.length }</AtTheBottomCenter>
  </>
}
```

## Combining multiple mdx files

Unlike the official `@mdx-js/loader`,
the `@mdx-deck/loader` exports an additional `slides` array of components instead of just the entire document.
Multiple MDX files can be combined into a single presentation if the filesize is getting difficult to manage.

First create a couple `.mdx` files like any other MDX Deck file, with `---` to separate the different slides.

```mdx
# one.mdx

---

This is the first file
```

```mdx
# two.mdx

---

This is the second file
```

Next, create a `.js` file to import and combine the two `.mdx` files.

```js
// deck.js
import { slides as one } from './one.mdx'
import { slides as two } from './two.mdx'

export const slides = [...one, ...two]
```

Then, point the MDX Deck CLI comment in your `package.json` to the `deck.js` file.

```json
"scripts": {
  "start": "mdx-deck deck.js"
}
```

## Custom webpack config

Webpack configuration files named `webpack.config.js` will automatically be merged with the built-in configuration,
using [webpack-merge](https://github.com/survivejs/webpack-merge).
To use a custom filename, pass the file path to the `--webpack` flag.

```js
// webpack.config.js example
module.exports = {
  module: {
    rules: [
      {
        test: /\.svg$/,
        use: [{ loader: 'babel-loader' }, { loader: 'react-svg-loader' }],
      },
    ],
  },
}
```

**Careful**: When overwriting the loader for `mdx` files, make sure to include the default loader from `@mdx-deck/loader`.

## Custom build setups

The core MDX Deck components can also be used in any React application,
such as [create-react-app][] or [next.js][].

See the [`@mdx-deck/components`](../packages/components) package for more.

[mdx]: https://mdxjs.com
[mdxprovider]: https://github.com/mdx-js/mdx/blob/master/docs/getting-started/index.md#mdxprovider
[create-react-app]: https://github.com/facebook/create-react-app
[next.js]: https://github.com/zeit/next.js/