Execute scripts on page navigation (view transitions) (#7786)

* Execute scripts on page navigation (view transitions)

* Update .changeset/sharp-seas-smile.md

Co-authored-by: Sarah Rainsberger <sarah@rainsberger.ca>

---------

Co-authored-by: Sarah Rainsberger <sarah@rainsberger.ca>

4 files changed, 61 insertions, 4 deletions

diff --git a/.changeset/sharp-seas-smile.md b/.changeset/sharp-seas-smile.md
new file mode 100644
index 000000000..1bc478e80
--- /dev/null
+++ b/.changeset/sharp-seas-smile.md
@@ -0,0 +1,15 @@
+---
+'astro': patch
+---
+
+Execute scripts when navigating to a new page.
+
+When navigating to an new page with client-side navigation, scripts are executed (and re-executed) so that any new scripts on the incoming page are run and the DOM can be updated.
+
+However, `type=module` scripts never re-execute in Astro, and will not do so in client-side routing. To support cases where you want to modify the DOM, a new `astro:load` event listener been added:
+
+```js
+document.addEventListener('astro:load', () => {
+  updateTheDOMSomehow();
+});
+```
diff --git a/packages/astro/components/ViewTransitions.astro b/packages/astro/components/ViewTransitions.astro
index d7703bc82..c2f9a7206 100644
--- a/packages/astro/components/ViewTransitions.astro
+++ b/packages/astro/components/ViewTransitions.astro
@@ -25,6 +25,7 @@ const { fallback = 'animate' } = Astro.props as Props;
 	const supportsViewTransitions = !!document.startViewTransition;
 	const transitionEnabledOnThisPage = () =>
 		!!document.querySelector('[name="astro-view-transitions-enabled"]');
+	const onload = () => document.dispatchEvent(new Event('astro:load'));
 
 	async function getHTML(href: string) {
 		const res = await fetch(href);
@@ -40,6 +41,23 @@ const { fallback = 'animate' } = Astro.props as Props;
 		return 'animate';
 	}
 
+	function runScripts() {
+		let wait = Promise.resolve();
+		for(const script of Array.from(document.scripts)) {
+			const s = document.createElement('script');
+			s.innerHTML = script.innerHTML;
+			for(const attr of script.attributes) {
+				if(attr.name === 'src') {
+					const p = new Promise(r => {s.onload = r});
+					wait = wait.then(() => p as any);
+				}
+				s.setAttribute(attr.name, attr.value);
+			}
+			script.replaceWith(s);
+		}
+		return wait;
+	}
+
 	const parser = new DOMParser();
 
 	async function updateDOM(dir: Direction, html: string, fallback?: Fallback) {
@@ -95,6 +113,8 @@ const { fallback = 'animate' } = Astro.props as Props;
 			await finished;
 		} finally {
 			document.documentElement.removeAttribute('data-astro-transition');
+			await runScripts();
+			onload();
 		}
 	}
 
@@ -171,5 +191,6 @@ const { fallback = 'animate' } = Astro.props as Props;
 				{ passive: true, capture: true }
 			);
 		});
+		addEventListener('load', onload)
 	}
 </script>
diff --git a/packages/astro/e2e/fixtures/view-transitions/src/pages/two.astro b/packages/astro/e2e/fixtures/view-transitions/src/pages/two.astro
index ec5b699d8..84b16f259 100644
--- a/packages/astro/e2e/fixtures/view-transitions/src/pages/two.astro
+++ b/packages/astro/e2e/fixtures/view-transitions/src/pages/two.astro
@@ -3,4 +3,10 @@ import Layout from '../components/Layout.astro';
 ---
 <Layout link="/two.css">
 	<p id="two">Page 2</p>
+	<article id="twoarticle"></article>
 </Layout>
+<script>
+	document.addEventListener('astro:load', () => {
+		document.getElementById('twoarticle')!.textContent = 'works';
+	}, { once: true });
+</script>
diff --git a/packages/astro/e2e/view-transitions.test.js b/packages/astro/e2e/view-transitions.test.js
index da5252709..d799b5ef3 100644
--- a/packages/astro/e2e/view-transitions.test.js
+++ b/packages/astro/e2e/view-transitions.test.js
@@ -128,10 +128,6 @@ test.describe('View Transitions', () => {
 	});
 
 	test('Stylesheets in the head are waited on', async ({ page, astro }) => {
-		page.addListener('console', (data) => {
-			console.log(data);
-		});
-
 		// Go to page 1
 		await page.goto(astro.resolveUrl('/one'));
 		let p = page.locator('#one');
@@ -143,4 +139,23 @@ test.describe('View Transitions', () => {
 		await expect(p, 'should have content').toHaveText('Page 2');
 		await expect(p, 'imported CSS updated').toHaveCSS('font-size', '24px');
 	});
+
+	test('astro:load event fires when navigating to new page', async ({ page, astro }) => {
+		// Go to page 1
+		await page.goto(astro.resolveUrl('/one'));
+		const p = page.locator('#one');
+		await expect(p, 'should have content').toHaveText('Page 1');
+
+		// go to page 2
+		await page.click('#click-two');
+		const article = page.locator('#twoarticle');
+		await expect(article, 'should have script content').toHaveText('works');
+	});
+
+	test('astro:load event fires when navigating directly to a page', async ({ page, astro }) => {
+		// Go to page 1
+		await page.goto(astro.resolveUrl('/two'));
+		const article = page.locator('#twoarticle');
+		await expect(article, 'should have script content').toHaveText('works');
+	});
 });