Components: Add withState higher-order component

blocks/library/html/index.js

@@ -7,7 +7,7 @@ import TextareaAutosize from 'react-autosize-textarea';
  * WordPress dependencies
  */
 import { __ } from '@wordpress/i18n';
-import { Component } from '@wordpress/element';
+import { withState } from '@wordpress/components';
 
 /**
  * Internal dependencies
@@ -41,60 +41,42 @@ registerBlockType( 'core/html', {
 		},
 	},
 
-	edit: class extends Component {
-		constructor() {
-			super( ...arguments );
-			this.preview = this.preview.bind( this );
-			this.edit = this.edit.bind( this );
-			this.state = {
-				preview: false,
-			};
-		}
-
-		preview() {
-			this.setState( { preview: true } );
-		}
-
-		edit() {
-			this.setState( { preview: false } );
-		}
-
-		render() {
-			const { preview } = this.state;
-			const { attributes, setAttributes, focus } = this.props;
-
-			return (
-				<div>
-					{ focus &&
-						<BlockControls key="controls">
-							<div className="components-toolbar">
-								<button className={ `components-tab-button ${ ! preview ? 'is-active' : '' }` } onClick={ this.edit }>
-									<span>HTML</span>
-								</button>
-								<button className={ `components-tab-button ${ preview ? 'is-active' : '' }` } onClick={ this.preview }>
-									<span>{ __( 'Preview' ) }</span>
-								</button>
-							</div>
-						</BlockControls>
-					}
-					{ preview ?
-						<div dangerouslySetInnerHTML={ { __html: attributes.content } } /> :
-						<TextareaAutosize
-							value={ attributes.content }
-							onChange={ ( event ) => setAttributes( { content: event.target.value } ) }
-						/>
-					}
-					{ focus &&
-						<InspectorControls key="inspector">
-							<BlockDescription>
-								<p>{ __( 'Add custom HTML code and preview it right here in the editor.' ) }</p>
-							</BlockDescription>
-						</InspectorControls>
-					}
+	edit: withState( {
+		preview: false,
+	} )( ( { attributes, setAttributes, setState, focus, preview } ) => [
+		focus && (
+			<BlockControls key="controls">
+				<div className="components-toolbar">
+					<button
+						className={ `components-tab-button ${ ! preview ? 'is-active' : '' }` }
+						onClick={ () => setState( { preview: false } ) }>
+						<span>HTML</span>
+					</button>
+					<button
+						className={ `components-tab-button ${ preview ? 'is-active' : '' }` }
+						onClick={ () => setState( { preview: true } ) }>
+						<span>{ __( 'Preview' ) }</span>
+					</button>
 				</div>
-			);
-		}
-	},
+			</BlockControls>
+		),
+		preview ?
+			<div
+				key="preview"
+				dangerouslySetInnerHTML={ { __html: attributes.content } } /> :
+			<TextareaAutosize
+				key="editor"
+				value={ attributes.content }
+				onChange={ ( event ) => setAttributes( { content: event.target.value } ) }
+			/>,
+		focus && (
+			<InspectorControls key="inspector">
+				<BlockDescription>
+					<p>{ __( 'Add custom HTML code and preview it right here in the editor.' ) }</p>
+				</BlockDescription>
+			</InspectorControls>
+		),
+	] ),
 
 	save( { attributes } ) {
 		return attributes.content;

components/higher-order/with-state/README.md

@@ -0,0 +1,32 @@
+withState
+=========
+
+`withState` is a React [higher-order component](https://facebook.github.io/react/docs/higher-order-components.html) which enables a function component to have internal state.
+
+Wrapping a component with `withState` provides state as props to the wrapped component, along with a `setState` updater function.
+
+## Usage
+
+```jsx
+/**
+ * WordPress dependencies
+ */
+import { withState } from '@wordpress/components';
+
+function MyCounter( { count, setState } ) {
+	return (
+		<>
+			Count: { count }
+			<button onClick={ () => setState( ( state ) => ( { count: state.count + 1 } ) ) }>
+				Increment
+			</button>
+		</>
+	);
+}
+
+export default withState( {
+	count: 0,
+} )( MyCounter );
+```
+
+`withState` optionally accepts an object argument to define the initial state. It returns a function which can then be used in composing your component.

components/higher-order/with-state/index.js

@@ -0,0 +1,41 @@
+/**
+ * WordPress dependencies
+ */
+import { Component, getWrapperDisplayName } from '@wordpress/element';
+
+/**
+ * A Higher Order Component used to provide and manage internal component state
+ * via props.
+ *
+ * @param  {?Object}   initialState Optional initial state of the component
+ * @return {Component}              Wrapped component
+ */
+function withState( initialState = {} ) {
+	return ( OriginalComponent ) => {
+		class WrappedComponent extends Component {
+			constructor() {
+				super( ...arguments );
+
+				this.setState = this.setState.bind( this );
+
+				this.state = initialState;
+			}
+
+			render() {
+				return (
+					<OriginalComponent
+						{ ...this.props }
+						{ ...this.state }
+						setState={ this.setState }
+					/>
+				);
+			}
+		}
+
+		WrappedComponent.displayName = getWrapperDisplayName( WrappedComponent, 'state' );
+
+		return WrappedComponent;
+	};
+}
+
+export default withState;

components/higher-order/with-state/test/index.js

@@ -0,0 +1,25 @@
+/**
+ * External dependencies
+ */
+import { mount } from 'enzyme';
+
+/**
+ * Internal dependencies
+ */
+import withState from '../';
+
+describe( 'withState', () => {
+	it( 'should pass initial state and allow updates', () => {
+		const EnhancedComponent = withState( { count: 0 } )( ( { count, setState } ) => (
+			<button onClick={ () => setState( ( state ) => ( { count: state.count + 1 } ) ) }>
+				{ count }
+			</button>
+		) );
+
+		const wrapper = mount( <EnhancedComponent /> );
+
+		expect( wrapper.html() ).toBe( '<button>0</button>' );
+		wrapper.find( 'button' ).simulate( 'click' );
+		expect( wrapper.html() ).toBe( '<button>1</button>' );
+	} );
+} );

components/index.js

@@ -44,3 +44,4 @@ export { default as withFocusOutside } from './higher-order/with-focus-outside';
 export { default as withFocusReturn } from './higher-order/with-focus-return';
 export { default as withInstanceId } from './higher-order/with-instance-id';
 export { default as withSpokenMessages } from './higher-order/with-spoken-messages';
+export { default as withState } from './higher-order/with-state';