Components: Optimize withFilters, avoiding per-instance bindings

packages/components/CHANGELOG.md

@@ -1,3 +1,10 @@
+## 7.1.0 (Unreleased)
+
+### Improvements
+
+- `withFilters` has been optimized to avoid binding hook handlers for each mounted instance of the component, instead using a single centralized hook delegator.
+- `withFilters` has been optimized to reuse a single shared component definition for all filtered instances of the component.
+
 ## 7.0.5 (2019-01-03)
 
 ## 7.0.4 (2018-12-12)

packages/components/src/higher-order/with-filters/index.js

@@ -1,7 +1,7 @@
 /**
  * External dependencies
  */
-import { debounce, uniqueId } from 'lodash';
+import { debounce, without } from 'lodash';
 
 /**
  * WordPress dependencies
@@ -24,45 +24,94 @@ const ANIMATION_FRAME_PERIOD = 16;
  */
 export default function withFilters( hookName ) {
 	return createHigherOrderComponent( ( OriginalComponent ) => {
-		return class FilteredComponent extends Component {
-			/** @inheritdoc */
-			constructor( props ) {
-				super( props );
-
-				this.onHooksUpdated = this.onHooksUpdated.bind( this );
-				this.Component = applyFilters( hookName, OriginalComponent );
-				this.namespace = uniqueId( 'core/with-filters/component-' );
-				this.throttledForceUpdate = debounce( () => {
-					this.Component = applyFilters( hookName, OriginalComponent );
-					this.forceUpdate();
-				}, ANIMATION_FRAME_PERIOD );
-
-				addAction( 'hookRemoved', this.namespace, this.onHooksUpdated );
-				addAction( 'hookAdded', this.namespace, this.onHooksUpdated );
+		const namespace = 'core/with-filters/' + hookName;
+
+		/**
+		 * The component definition with current filters applied. Each instance
+		 * reuse this shared reference as an optimization to avoid excessive
+		 * calls to `applyFilters` when many instances exist.
+		 *
+		 * @type {?Component}
+		 */
+		let FilteredComponent;
+
+		/**
+		 * Initializes the FilteredComponent variable once, if not already
+		 * assigned. Subsequent calls are effectively a noop.
+		 */
+		function ensureFilteredComponent() {
+			if ( FilteredComponent === undefined ) {
+				FilteredComponent = applyFilters( hookName, OriginalComponent );
 			}
+		}
 
-			/** @inheritdoc */
-			componentWillUnmount() {
-				this.throttledForceUpdate.cancel();
-				removeAction( 'hookRemoved', this.namespace );
-				removeAction( 'hookAdded', this.namespace );
+		class FilteredComponentRenderer extends Component {
+			constructor() {
+				super( ...arguments );
+
+				ensureFilteredComponent();
+			}
+
+			componentDidMount() {
+				FilteredComponentRenderer.instances.push( this );
+
+				// If there were previously no mounted instances for components
+				// filtered on this hook, add the hook handler.
+				if ( FilteredComponentRenderer.instances.length === 1 ) {
+					addAction( 'hookRemoved', namespace, onHooksUpdated );
+					addAction( 'hookAdded', namespace, onHooksUpdated );
+				}
 			}
 
-			/**
-			 * When a filter is added or removed for the matching hook name, the wrapped component should re-render.
-			 *
-			 * @param {string} updatedHookName  Name of the hook that was updated.
-			 */
-			onHooksUpdated( updatedHookName ) {
-				if ( updatedHookName === hookName ) {
-					this.throttledForceUpdate();
+			componentWillUnmount() {
+				FilteredComponentRenderer.instances = without(
+					FilteredComponentRenderer.instances,
+					this
+				);
+
+				// If this was the last of the mounted components filtered on
+				// this hook, remove the hook handler.
+				if ( FilteredComponentRenderer.instances.length === 0 ) {
+					removeAction( 'hookRemoved', namespace );
+					removeAction( 'hookAdded', namespace );
 				}
 			}
 
-			/** @inheritdoc */
 			render() {
-				return <this.Component { ...this.props } />;
+				return <FilteredComponent { ...this.props } />;
+			}
+		}
+
+		FilteredComponentRenderer.instances = [];
+
+		/**
+		 * Updates the FilteredComponent definition, forcing a render for each
+		 * mounted instance. This occurs a maximum of once per animation frame.
+		 */
+		const throttledForceUpdate = debounce( () => {
+			// Recreate the filtered component, only after delay so that it's
+			// computed once, even if many filters added.
+			FilteredComponent = applyFilters( hookName, OriginalComponent );
+
+			// Force each instance to render.
+			FilteredComponentRenderer.instances.forEach( ( instance ) => {
+				instance.forceUpdate();
+			} );
+		}, ANIMATION_FRAME_PERIOD );
+
+		/**
+		 * When a filter is added or removed for the matching hook name, each
+		 * mounted instance should re-render with the new filters having been
+		 * applied to the original component.
+		 *
+		 * @param {string} updatedHookName Name of the hook that was updated.
+		 */
+		function onHooksUpdated( updatedHookName ) {
+			if ( updatedHookName === hookName ) {
+				throttledForceUpdate();
 			}
-		};
+		}
+
+		return FilteredComponentRenderer;
 	}, 'withFilters' );
 }