docs/extending.md
# Extending With Widgets
The NetlifyCMS exposes an `window.CMS` global object that you can use to register custom widgets, previews, and editor plugins. The available widget extension methods are:
* **registerWidget:** lets you register a custom widget.
* **registerEditorComponent:** lets you add a block component to the Markdown editor.
### Writing React Components inline
The `registerWidget` requires you to provide a React component. If you have a build process in place for your project, it is possible to integrate with this build process.
However, although possible, it may be cumbersome or even impractical to add a React build phase. For this reason, NetlifyCMS exposes two constructs globally to allow you to create components inline: ‘createClass’ and ‘h’ (alias for React.createElement).
## `registerWidget`
Register a custom widget.
```js
CMS.registerWidget(name, control, \[preview\])
```
**Params:**
Param | Type | Description
--- | --- | ---
`name` | string | Widget name, allows this widget to be used via the field `widget` property in config
`control` | React.Component \| string | <ul><li>React component that renders the control, receives the following props: <ul><li>**value:** Current field value</li><li>**onChange:** Callback function to update the field value</li></ul></li><li>Name of a registered widget whose control should be used (includes built in widgets).</li></ul>
[`preview`] | React.Component, optional | Renders the widget preview, receives the following props: <ul><li>**value:** Current preview value</li><li>**field:** Immutable map of current field configuration</li><li>**metadata:** Immutable map of any available metadata for the current field</li><li>**getAsset:** Function for retrieving an asset url for image/file fields</li><li>**entry:** Immutable Map of all entry data</li><li>**fieldsMetaData:** Immutable map of metadata from all fields.</li></ul>
* **field:** The field type that this widget will be used for.
* **control:** A React component that renders the editing interface for this field. Two props will be passed:
* **value:** The current value for this field.
* **onChange:** Callback function to update the field value.
* **preview (optional):** A React component that renders the preview of how the content will look. A `value` prop will be passed to this component.
**Example:**
```html
<script src="https://unpkg.com/netlify-cms@~0.4/dist/cms.js"></script>
<script>
var CategoriesControl = createClass({
handleChange: function(e) {
this.props.onChange(e.target.value.split(',').map((e) => e.trim()));
},
render: function() {
var value = this.props.value;
return h('input', { type: 'text', value: value ? value.join(', ') : '', onChange: this.handleChange });
}
});
var CategoriesPreview = createClass({
render: function() {
return h('ul', {},
this.props.value.map(function(val, index) {
return h('li', {key: index}, val);
})
);
}
});
CMS.registerWidget('categories', CategoriesControl, CategoriesPreview);
</script>
```
## `registerEditorComponent`
Register a block level component for the Markdown editor:
CMS.registerEditorComponent(definition)
**Params**
* **definition:** The component definition; must specify: id, label, fields, patterns, fromBlock, toBlock, toPreview
**Example:**
```html
<script src="https://unpkg.com/netlify-cms@~0.4/dist/cms.js"></script>
<script>
CMS.registerEditorComponent({
// Internal id of the component
id: "youtube",
// Visible label
label: "Youtube",
// Fields the user need to fill out when adding an instance of the component
fields: [{name: 'id', label: 'Youtube Video ID', widget: 'string'}],
// Pattern to identify a block as being an instance of this component
pattern: youtube (\S+)\s,
// Function to extract data elements from the regexp match
fromBlock: function(match) {
return {
id: match[1]
};
},
// Function to create a text block from an instance of this component
toBlock: function(obj) {
return 'youtube ' + obj.id;
},
// Preview output for this component. Can either be a string or a React component
// (component gives better render performance)
toPreview: function(obj) {
return (
'<img src="http://img.youtube.com/vi/' + obj.id + '/maxresdefault.jpg" alt="Youtube Video"/>'
);
}
});
</script>
```
**Result:**
