The NetlifyCMS exposes a window.CMS a global object that you can use to register custom widgets, previews, and editor plugins. The same object is also the default export if you import Netlify CMS as an npm module. The available widget extension methods are:

• registerWidget: registers a custom widget.
• registerEditorComponent: adds 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.

// Using global window object
CMS.registerWidget(name, control, [preview], [schema]);

// Using npm module import
import CMS from 'netlify-cms';
CMS.registerWidget(name, control, [preview], [schema]);

Params:

Example:

admin/index.html

<script src="https://unpkg.com/netlify-cms@^2.0.0/dist/netlify-cms.js"></script>
<script>
var CategoriesControl = createClass({
  handleChange: function(e) {
    const separator = this.props.field.get('separator', ', ')
    this.props.onChange(e.target.value.split(separator).map((e) => e.trim()));
  },

  render: function() {
    const separator = this.props.field.get('separator', ', ');
    var value = this.props.value;
    return h('input', {
      id: this.props.forID,
      className: this.props.classNameWrapper,
      type: 'text',
      value: value ? value.join(separator) : '',
      onChange: this.handleChange,
    });
  },
});

var CategoriesPreview = createClass({
  render: function() {
    return h('ul', {},
      this.props.value.map(function(val, index) {
        return h('li', {key: index}, val);
      })
    );
  }
});

var schema = {
  properties: {
    separator: { type: 'string' },
  },
}

CMS.registerWidget('categories', CategoriesControl, CategoriesPreview, schema);
</script>

admin/config.yml

collections:
  - name: posts
    label: Posts
    folder: content/posts
    fields:
      - name: title
        label: Title
        widget: string
      - name: categories
        label: Categories
        widget: categories
        separator: __

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

Additional properties are optional and will be passed to the underlying widget control (object widget by default). For example, adding a collapsed: true property will collapse the widget by default.

Example:

<script src="https://unpkg.com/netlify-cms@^2.0.0/dist/netlify-cms.js"></script>
<script>
CMS.registerEditorComponent({
  // Internal id of the component
  id: "collapsible-note",
  // Visible label
  label: "Collapsible Note",
  // Fields the user need to fill out when adding an instance of the component
  fields: [
    {
      name: 'summary',
      label: 'Summary',
      widget: 'string'
    },
    {
      name: 'details',
      label: 'Details',
      widget: 'markdown'
    }
  ],
  // Regex pattern used to search for instances of this block in the markdown document.
  // Patterns are run in a multline environment (against the entire markdown document),
  // and so generally should make use of the multiline flag (`m`). If you need to capture
  // newlines in your capturing groups, you can either use something like
  // `([\S\s]*)`, or you can additionally enable the "dot all" flag (`s`),
  // which will cause `(.*)` to match newlines as well.
  //
  // Additionally, it's recommended that you use non-greedy capturing groups (e.g.
  // `(.*?)` vs `(.*)`), especially if matching against newline characters.
  pattern: /^<details>$\s*?<summary>(.*?)<\/summary>\n\n(.*?)\n^<\/details>$/ms,
  // Given a RegExp Match object
  // (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/match#return_value),
  // return an object with one property for each field defined in `fields`.
  //
  // This is used to populate the custom widget in the markdown editor in the CMS.
  fromBlock: function(match) {
    return {
      summary: match[1],
      detail: match[2]
    };
  },
  // Given an object with one property for each field defined in `fields`,
  // return the string you wish to be inserted into your markdown.
  //
  // This is used to serialize the data from the custom widget to the
  // markdown document
  toBlock: function(data) {
    return `
<details>
  <summary>${data.summary}</summary>

  ${data.detail}

</details>
`;
  },
  // Preview output for this component. Can either be a string or a React component
  // (component gives better render performance)
  toPreview: function(data) {
    return `
<details>
  <summary>${data.summary}</summary>

  ${data.detail}

</details>
`;
  }
});
</script>

Result:

Advanced field validation

All widget fields, including those for built-in widgets, include basic validation capability using the required and pattern options.

With custom widgets, the widget control can also optionally implement an isValid method to perform custom validations, in addition to presence and pattern. The isValid method will be automatically called, and it can return either a boolean value, an object with an error message or a promise. Examples:

Boolean No errors:

  isValid = () => {
    // Do internal validation
    return true;
  };

Existing error:

  isValid = () => {
    // Do internal validation
    return false;
  };

Object with error (useful for returning custom error messages) Existing error:

  isValid = () => {
    // Do internal validation
    return { error: { message: 'Your error message.' } };
  };

Promise You can also return a promise from isValid. While the promise is pending, the widget will be marked as “in error”. When the promise resolves, the error is automatically cleared.

  isValid = () => {
    return this.existingPromise;
  };

Note: Do not create a promise inside isValid - isValid is called right before trying to persist. This means that even if a previous promise was already resolved, when the user hits ‘save’, isValid will be called again. If it returns a new promise, it will be immediately marked as “in error” until the new promise resolves.

Writing custom widgets as a separate package

Widgets are inputs for the Netlify CMS editor interface. It’s a React component that receives user input and outputs a serialized value. Those are the only rules - the component can be extremely simple, like text input, or extremely complicated, like a full-blown markdown editor. They can make calls to external services, and generally do anything that JavaScript can do.

For writing custom widgets as a separate package you should follow these steps:

1. Create a directory

   mkdir my-custom-widget
   

2. Navigate to the directory

   cd my-custom-widget
   

3. For setting up a new npm package run this command:

   npm init
   

4. Answer the questions in the command line questionnaire.
5. In order to build React components, we need to set up a build step. We’ll be using Webpack. Please run the following commands to install the required dependencies:

   npm install --save-dev babel-loader@7 babel-core babel-plugin-transform-class-properties babel-plugin-transform-export-extensions babel-plugin-transform-object-rest-spread babel-preset-env babel-preset-react cross-env css-loader html-webpack-plugin netlify-cms react source-map-loader style-loader webpack webpack-cli webpack-serve

   npm install --save prop-types

And you should manually add “peerDependencies” and “scripts” as shown below.

Here is the content of package.json that you will have at the end:

{
  "name": "netlify-cms-widget-starter",
  "description": "A boilerplate for creating Netlify CMS widgets.",
  "author": "name of developer",
  "keywords": [
    "netlify",
    "netlify-cms",
    "cms",
    "widget",
    "starter",
    "boilerplate"
  ],
  "version": "0.0.1",
  "homepage": "https://github.com/netlify/netlify-cms-widget-starter",
  "license": "MIT",
  "main": "dist/main.js",
  "devDependencies": {
    "babel-loader": "^7.1.4",
    "babel-plugin-transform-class-properties": "^6.24.1",
    "babel-plugin-transform-export-extensions": "^6.22.0",
    "babel-plugin-transform-object-rest-spread": "^6.26.0",
    "babel-preset-env": "^1.6.1",
    "babel-preset-react": "^6.24.1",
    "cross-env": "^5.1.4",
    "css-loader": "^0.28.11",
    "html-webpack-plugin": "^3.2.0",
    "netlify-cms": "^1.5.0",
    "react": "^16.3.2",
    "source-map-loader": "^0.2.3",
    "style-loader": "^0.20.3",
    "webpack": "^4.6.0",
    "webpack-cli": "^2.0.14",
    "webpack-serve": "^0.3.1"
  },
  "dependencies": {
    "prop-types": "^15.6.1"
  },
  "peerDependencies": {
    "react": "^16"
  },
  "scripts": {
    "start": "webpack-serve --static public --open"
  }
}

1. Create a Webpack configuration file with this content:

   webpack.config.js

   const path = require('path')
   const HtmlWebpackPlugin = require('html-webpack-plugin')
   
   const developmentConfig = {
     mode: 'development',
     entry: './dev/index.js',
     output: {
       path: path.resolve(__dirname, 'public'),
     },
     optimization: { minimize: false },
     module: {
       rules: [
         {
           test: /\.js$/,
           loader: 'source-map-loader',
           enforce: 'pre',
         },
         {
           test: /\.jsx?$/,
           exclude: /node_modules/,
           loader: 'babel-loader',
         },
         {
           test: /\.css$/,
           use: [{ loader: 'style-loader' }, { loader: 'css-loader' }],
         },
       ],
     },
     plugins: [
       new HtmlWebpackPlugin(),
     ],
     devtool: 'eval-source-map',
   }
   
   const productionConfig = {
     mode: 'production',
     module: {
       rules: [
         {
           test: /\.jsx?$/,
           loader: 'babel-loader',
         },
       ],
     },
     devtool: 'source-map',
   }
   
   module.exports = process.env.NODE_ENV === 'production' ? productionConfig : developmentConfig
   

2. The .babelrc file is our local configuration for our code in the project. You should create it under the root of the application repo. It will affect all files that Babel processes. So, create a .babelrc file under the main project with this content:

{
  "presets": [
    "react",
    "env",
  ],
  "plugins": [
    "transform-export-extensions",
    "transform-class-properties",
    "transform-object-rest-spread",
  ],
}

1. Create a src directory with the files Control.js, Preview.js and index.js

src/Control.js

 import PropTypes from 'prop-types';
 import React from 'react';

 export default class Control extends React.Component {
   static propTypes = {
     onChange: PropTypes.func.isRequired,
     forID: PropTypes.string,
     value: PropTypes.node,
     classNameWrapper: PropTypes.string.isRequired,
   }

   static defaultProps = {
     value: '',
   }

   render() {
     const {
       forID,
       value,
       onChange,
       classNameWrapper,
     } = this.props;

     return (
       <input
         type="text"
         id={forID}
         className={classNameWrapper}
         value={value || ''}
         onChange={e => onChange(e.target.value)}
       />
     );
   }
 }

src/Preview.js

import PropTypes from 'prop-types';
import React from 'react';

export default function Preview({ value }) {
  return <div>{ value }</div>;
}

Preview.propTypes = {
  value: PropTypes.node,
};

src/index.js

import Control from './Control'
import Preview from './Preview'

if (typeof window !== 'undefined') {
  window.Control = Control
  window.Preview = Preview
}

export { Control, Preview }

1. Now you need to set up the locale example site. Under the main project, create a dev directory with the files bootstrap.js and index.js

bootstrap.js

window.CMS_MANUAL_INIT = true

index.js

import './bootstrap.js'
import CMS, { init } from 'netlify-cms'
import 'netlify-cms/dist/cms.css'
import { Control, Preview } from '../src'

const config = {
backend: {
 name: 'test-repo',
 login: false,
},
media_folder: 'assets',
collections: [{
 name: 'test',
 label: 'Test',
 files: [{
   file: 'test.yml',
   name: 'test',
   label: 'Test',
   fields: [
     { name: 'test_widget', label: 'Test Widget', widget: 'test'},
   ],
 }],
}],
}

CMS.registerWidget('test', Control, Preview)

init({ config })

Development

To run a copy of Netlify CMS with your widget for development, use the start script:

npm start

Your widget source is in the src directory, where there are separate files for the Control and Preview components.

Production & Publishing

You’ll want to take a few steps before publishing a production built package to npm:

1. Customize package.json with details for your specific widget, e.g. name, description, author, version, etc.

   {
     "name": "netlify-cms-widget-starter",
     "description": "A boilerplate for creating Netlify CMS widgets.",
     "author": "name of developer",
     "keywords": [
       "netlify",
       "netlify-cms",
       "cms",
       "widget",
       "starter",
       "boilerplate"
     ],
     "version": "0.0.1",
     // ... rest
   }
   

2. For discoverability, ensure that your package name follows the pattern netlify-cms-widget-<name>.
3. Delete this README.md, rename README_TEMPLATE.md to README.md, and update the new file for your specific widget.
4. Rename the exports in src/index.js. For example, if your widget is netlify-cms-widget-awesome, you would do:

if (typeof window !== 'undefined') {
  window.AwesomeControl = Control
  window.AwesomePreview = Preview
}

export { Control as AwesomeControl, Preview as AwesomePreview }

1. Optional: customize the component and file names in src.
2. If you haven’t already, push your repo to your GitHub account so the source available to other developers.
3. Create a production build, which will be output to dist:

npm run build

1. Finally, if you’re sure things are tested and working, publish!

npm publish