static-cms/docs/customization.md

# Customizing the Preview Pane

The NetlifyCMS exposes a `window.CMS` global object that you can use to register custom widgets, previews and editor plugins. The available customization methods are:

* **registerPreviewStyle:** Register a custom stylesheet to use on the preview pane.
* **registerPreviewTemplate:** Registers a template for a collection.

Explore the [NetlifyCMS GitHub example](https://github.com/netlify/netlify-cms/blob/9ced3f16c8bcc3d1a36773b126842d023c589eaf/example/index.html#L90-L91), a working example you can review on GitHub.

### React Components inline interaction

NetlifyCMS is a collection of React components and exposes two constructs globally to allow you to create components inline: ‘createClass’ and ‘h’ (alias for React.createElement).

## `registerPreviewStyle`

Register a custom stylesheet to use on the preview pane.

```js
CMS.registerPreviewStyle(file);
```

**Params:**

* **file:** css file path

**Example:**
```html
// index.html
<script src="https://unpkg.com/netlify-cms@~0.4/dist/cms.js"></script>
<script>
  CMS.registerPreviewStyle("/example.css");
</script>
```
```css
/* example.css */

html,
body {
  color: #444;
  font-size: 14px;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
}

body {
  padding: 20px;
}


```


## `registerPreviewTemplate`

Registers a template for a collection.

`CMS.registerPreviewTemplate(collection, react_component);`

**Params:**

* collection: The name of the collection which this preview component will be used for.
* react_component: A React component that renders the collection data. Four props will be passed to your component during render:
  * entry: Immutable collection containing the entry data.
  * widgetFor: Returns the appropriate widget preview component for a given field.
  * [widgetsFor](#lists-and-objects): Returns an array of objects with widgets and associated field data. For use with list and object type entries.
  * getAsset: Returns the correct filePath or in-memory preview for uploaded images.
    
    **Example:**
    
    ```html
    <script src="https://unpkg.com/netlify-cms@~0.4/dist/cms.js"></script>
    <script>
    var PostPreview = createClass({
      render: function() {
        var entry = this.props.entry;
        var image = entry.getIn(['data', 'image']);
        var bg = this.props.getAsset(image);
        return h('div', {},
          h('h1', {}, entry.getIn(['data', 'title'])),
          h('img', {src: bg.toString()}),
          h('div', {"className": "text"}, this.props.widgetFor('body'))
        );
      }
    });
    
    CMS.registerPreviewTemplate("posts", PostPreview);
    </script>
    ```
    
    ### Lists and Objects
    The API for accessing the individual fields of list- and object-type entries is similar to the API
    for accessing fields in standard entries, but there are a few key differences. Access to these
    nested fields is facilitated through the `widgetsFor` function, which is passed to the preview
    template component during render.
    
    **Note**: as is often the case with the NetlifyCMS API, arrays and objects are created with
    Immutable.js. If some of the methods that we use are unfamiliar, such as `getIn`, check out
    [their docs](https://facebook.github.io/immutable-js/docs/#/) to get a better understanding.
    
    **List Example:**
    
    ```html
    <script>
    var AuthorsPreview = createClass({
      // For list fields, the widgetFor function returns an array of objects
      // that you can map over in your template. If our field is a list of
      // authors containing two entries, with fields `name` and `description`,
      // the return value of `widgetsFor` would look like this:
      //
      // [{
      //   data: { name: 'Mathias', description: 'Co-Founder'},
      //   widgets: { name: (<WidgetComponent>), description: (WidgetComponent>)}
      // },
      // {
      //   data: { name: 'Chris', description: 'Co-Founder'},
      //   widgets: { name: (<WidgetComponent>), description: (WidgetComponent>)}
      // }]
      //
      // Templating would look something like this:
    
      render: function() {
        return h('div', {},
    
          // This is a static header that would only be rendered once for the entire list
          h('h1', {}, 'Authors'),
    
          // Here we provide a simple mapping function that will be applied to each
          // object in the array of authors
          this.props.widgetsFor('authors').map(function(author, index) {
            return h('div', {key: index},
              h('hr', {}),
              h('strong', {}, author.getIn(['data', 'name'])),
              author.getIn(['widgets', 'description'])
            );
          })
        );
      }
    });
    
    CMS.registerPreviewTemplate("authors", AuthorsPreview);
    </script>
    ```
    
    **Object Example:**
    
    ```html
    <script>
    var GeneralPreview = createClass({
      // Object fields are simpler than lists - instead of `widgetsFor` returning
      // an array of objects, it returns a single object. Accessing the shape of
      // that object is the same as the shape of objects returned for list fields:
      //
      // {
      //   data: { front_limit: 0, author: 'Chris' },
      //   widgets: { front_limit: (<WidgetComponent>), author: (WidgetComponent>)}
      // }
      render: function() {
        var entry = this.props.entry;
        var title = entry.getIn(['data', 'site_title']);
        var posts = entry.getIn(['data', 'posts']);
    
        return h('div', {},
          h('h1', {}, title),
          h('dl', {},
            h('dt', {}, 'Posts on Frontpage'),
            h('dd', {}, this.props.widgetsFor('posts').getIn(['widgets', 'front_limit']) || 0),
    
            h('dt', {}, 'Default Author'),
            h('dd', {}, this.props.widgetsFor('posts').getIn(['data', 'author']) || 'None'),
          )
        );
      }
    });
    
    CMS.registerPreviewTemplate("general", GeneralPreview);
    </script>
    ```
    
    ### Accessing Metadata
    Preview Components also receive an additional prop: `fieldsMetaData`. It contains aditional information (besides the plain plain textual value of each field) that can be useful for preview purposes. 
    
    For example, the Relation widget passes the whole selected relation data in `fieldsMetaData`.
    
    ```js
    export default class ArticlePreview extends React.Component {
      render() {
        const {entry, fieldsMetaData} = this.props;
        const author = fieldsMetaData.getIn(['authors', data.author]);
    
        return <article><h2>{ entry.getIn(['data', 'title']) }</h2>
          {author &&<AuthorBio author={author.toJS()}/>}
        </article>
      }
    }
    ```