Components: Update ExternalLink to support onClick handler (#45214)

* Update ExternalLink to support onClick handler

* Add unit tests for ExternalLink component

It includes test cases for onClick event handler and preventing default action when clicking internal anchor links.

* Test using getByRole and userEvent

* Add CHANGELOG entry

* Add comments for defaultPrevented approach

* Remove unnecessary data-testid attributes

packages/components/CHANGELOG.md

@@ -34,6 +34,7 @@
 -   `TabPanel`: Call `onSelect()` on every tab selection, regardless of whether it was triggered by user interaction ([#44028](https://github.com/WordPress/gutenberg/pull/44028)).
 -   `FontSizePicker`: Fallback to font size `slug` if `name` is undefined  ([#45041](https://github.com/WordPress/gutenberg/pull/45041)).
 -   `AutocompleterUI`: fix issue where autocompleter UI would appear on top of other UI elements ([#44795](https://github.com/WordPress/gutenberg/pull/44795/))
+-   `ExternalLink`: Fix to re-enable support for `onClick` event handler ([#45214](https://github.com/WordPress/gutenberg/pull/45214)).
 
 ### Internal
 

packages/components/src/external-link/index.tsx

@@ -43,17 +43,25 @@ function UnforwardedExternalLink(
 	to prevent them from being opened in the editor. */
 	const isInternalAnchor = !! href?.startsWith( '#' );
 
+	const onClickHandler = (
+		event: React.MouseEvent< HTMLAnchorElement, MouseEvent >
+	) => {
+		if ( isInternalAnchor ) {
+			event.preventDefault();
+		}
+
+		if ( props.onClick ) {
+			props.onClick( event );
+		}
+	};
+
 	return (
 		/* eslint-disable react/jsx-no-target-blank */
 		<a
 			{ ...additionalProps }
 			className={ classes }
 			href={ href }
-			onClick={
-				isInternalAnchor
-					? ( event ) => event.preventDefault()
-					: undefined
-			}
+			onClick={ onClickHandler }
 			target="_blank"
 			rel={ optimizedRel }
 			ref={ ref }

packages/components/src/external-link/test/index.tsx

@@ -0,0 +1,106 @@
+/**
+ * External dependencies
+ */
+import { render, screen } from '@testing-library/react';
+import userEvent from '@testing-library/user-event';
+
+/**
+ * Internal dependencies
+ */
+import { ExternalLink } from '..';
+
+const setupUser = () =>
+	userEvent.setup( {
+		advanceTimers: jest.advanceTimersByTime,
+	} );
+
+describe( 'ExternalLink', () => {
+	test( 'should call function passed in onClick handler when clicking the link', async () => {
+		const user = setupUser();
+		const onClickMock = jest.fn();
+
+		render(
+			<ExternalLink href="https://wordpress.org" onClick={ onClickMock }>
+				WordPress.org
+			</ExternalLink>
+		);
+
+		const link = screen.getByRole( 'link', {
+			name: 'WordPress.org (opens in a new tab)',
+		} );
+
+		await user.click( link );
+
+		expect( onClickMock ).toHaveBeenCalledTimes( 1 );
+	} );
+
+	test( 'should prevent default action when clicking an internal anchor link without passing onClick prop', async () => {
+		const user = setupUser();
+
+		render(
+			<ExternalLink href="#test">I&apos;m an anchor link!</ExternalLink>
+		);
+
+		const link = screen.getByRole( 'link', {
+			name: "I'm an anchor link! (opens in a new tab)",
+		} );
+
+		// We are using this approach so we can test the defaultPrevented
+		// without passing an onClick prop to the component.
+		const onClickMock = jest.fn();
+		link.onclick = onClickMock;
+
+		await user.click( link );
+		expect( onClickMock ).toHaveBeenCalledTimes( 1 );
+		expect( onClickMock ).toHaveBeenLastCalledWith(
+			expect.objectContaining( { defaultPrevented: true } )
+		);
+	} );
+
+	test( 'should call function passed in onClick handler and prevent default action when clicking an internal anchor link', async () => {
+		const user = setupUser();
+		const onClickMock = jest.fn();
+
+		render(
+			<ExternalLink href="#test" onClick={ onClickMock }>
+				I&apos;m an anchor link!
+			</ExternalLink>
+		);
+
+		const link = screen.getByRole( 'link', {
+			name: "I'm an anchor link! (opens in a new tab)",
+		} );
+
+		await user.click( link );
+		expect( onClickMock ).toHaveBeenCalledTimes( 1 );
+		expect( onClickMock ).toHaveBeenLastCalledWith(
+			expect.objectContaining( { defaultPrevented: true } )
+		);
+	} );
+
+	test( 'should not prevent default action when clicking a non anchor link without passing onClick prop', async () => {
+		const user = setupUser();
+
+		render(
+			<ExternalLink href="https://wordpress.org">
+				I&apos;m not an anchor link!
+			</ExternalLink>
+		);
+
+		const link = screen.getByRole( 'link', {
+			name: "I'm not an anchor link! (opens in a new tab)",
+		} );
+
+		// We are using this approach so we can test the defaultPrevented
+		// without passing an onClick prop to the component.
+		const onClickMock = jest.fn();
+		link.onclick = onClickMock;
+
+		await user.click( link );
+
+		expect( onClickMock ).toHaveBeenCalledTimes( 1 );
+		expect( onClickMock ).toHaveBeenLastCalledWith(
+			expect.objectContaining( { defaultPrevented: false } )
+		);
+	} );
+} );