components: Add useLatestRef hook

packages/components/src/utils/hooks/index.js

@@ -3,3 +3,4 @@ export { default as useJumpStep } from './use-jump-step';
 export { default as useUpdateEffect } from './use-update-effect';
 export { useControlledValue } from './use-controlled-value';
 export { useCx } from './use-cx';
+export { useLatestRef } from './use-latest-ref';

packages/components/src/utils/hooks/test/use-latest-ref.js

@@ -0,0 +1,120 @@
+/**
+ * External dependencies
+ */
+import { render, screen, fireEvent, waitFor } from '@testing-library/react';
+
+/**
+ * WordPress dependencies
+ */
+import { useState } from '@wordpress/element';
+
+/**
+ * Internal dependencies
+ */
+import { useLatestRef } from '..';
+
+function debounce( callback, timeout = 0 ) {
+	let timeoutId = 0;
+	return ( ...args ) => {
+		window.clearTimeout( timeoutId );
+		timeoutId = window.setTimeout( () => callback( ...args ), timeout );
+	};
+}
+
+function useDebounce( callback, timeout = 0 ) {
+	const callbackRef = useLatestRef( callback );
+	return debounce( ( ...args ) => callbackRef.current( ...args ), timeout );
+}
+
+function Example() {
+	const [ count, setCount ] = useState( 0 );
+	const increment = () => setCount( count + 1 );
+	const incrementDebounced = debounce( increment, 50 );
+	const incrementDebouncedWithLatestRef = useDebounce( increment, 50 );
+
+	return (
+		<>
+			<div>Count: { count }</div>
+			<button onClick={ incrementDebounced }>Increment debounced</button>
+			<button onClick={ increment }>Increment immediately</button>
+			<br />
+			<button onClick={ incrementDebouncedWithLatestRef }>
+				Increment debounced with latest ref
+			</button>
+		</>
+	);
+}
+
+function sleep( milliseconds ) {
+	return new Promise( ( resolve ) =>
+		window.setTimeout( resolve, milliseconds )
+	);
+}
+
+function getCount() {
+	return screen.getByText( /Count:/ ).innerHTML;
+}
+
+function incrementCount() {
+	fireEvent.click( screen.getByText( 'Increment immediately' ) );
+}
+
+function incrementCountDebounced() {
+	fireEvent.click( screen.getByText( 'Increment debounced' ) );
+}
+
+function incrementCountDebouncedRef() {
+	fireEvent.click(
+		screen.getByText( 'Increment debounced with latest ref' )
+	);
+}
+
+describe( 'useLatestRef', () => {
+	describe( 'Example', () => {
+		// prove the example works as expected
+		it( 'should start at 0', () => {
+			render( <Example /> );
+			expect( getCount() ).toEqual( 'Count: 0' );
+		} );
+
+		it( 'should increment immediately', () => {
+			render( <Example /> );
+			incrementCount();
+			expect( getCount() ).toEqual( 'Count: 1' );
+		} );
+
+		it( 'should increment after debouncing', async () => {
+			render( <Example /> );
+			incrementCountDebounced();
+			expect( getCount() ).toEqual( 'Count: 0' );
+
+			await waitFor( () => sleep( 0 ) );
+			expect( getCount() ).toEqual( 'Count: 1' );
+		} );
+
+		it( 'should increment after debouncing with latest ref', async () => {
+			render( <Example /> );
+			incrementCountDebouncedRef();
+			expect( getCount() ).toEqual( 'Count: 0' );
+
+			await waitFor( () => sleep( 0 ) );
+			expect( getCount() ).toEqual( 'Count: 1' );
+		} );
+	} );
+
+	it( 'should increment to one', async () => {
+		render( <Example /> );
+		incrementCountDebounced();
+		incrementCount();
+		await waitFor( () => sleep( 0 ) );
+		expect( getCount() ).toEqual( 'Count: 1' );
+	} );
+
+	it( 'should increment to two', async () => {
+		render( <Example /> );
+		incrementCountDebouncedRef();
+		incrementCount();
+		await waitFor( () => sleep( 0 ) );
+		expect( getCount() ).toEqual( 'Count: 2' );
+	} );
+} );

packages/components/src/utils/hooks/use-latest-ref.ts

@@ -0,0 +1,30 @@
+/**
+ * External dependencies
+ */
+// eslint-disable-next-line no-restricted-imports
+import type { RefObject } from 'react';
+
+/**
+ * WordPress dependencies
+ */
+import { useRef } from '@wordpress/element';
+import { useIsomorphicLayoutEffect } from '@wordpress/compose';
+
+/**
+ * Creates a reference for a prop. This is useful for preserving dependency
+ * memoization for hooks like useCallback.
+ *
+ * @see https://codesandbox.io/s/uselatestref-mlj3i?file=/src/App.tsx
+ *
+ * @param  value The value to reference
+ * @return The prop reference.
+ */
+export function useLatestRef< T >( value: T ): RefObject< T > {
+	const ref = useRef( value );
+
+	useIsomorphicLayoutEffect( () => {
+		ref.current = value;
+	} );
+
+	return ref;
+}