enhance(prefetch): Adds a 'load' prefetch strategy, and ignores `3g…

…` in slow connection detection (#9513)

* [enhance:prefetch] add global ignoreSlowConnection and add none to defaultStrategy enum

* changeset

* change defaultStrategy enum 'none' to 'all', and fix e2e test

* test:e2e prefetch

* update changeset

* rename defaultStrategy.all to defaultStrategy.load

* fix: remove global ignoreSlowConnection config and ignore 3g in slow connection detection

* fix: Revert variable name changes

* Split changeset

---------

Co-authored-by: bluwy <bjornlu.dev@gmail.com>
Co-authored-by: Emanuele Stoppa <my.burning@gmail.com>
Co-authored-by: Sarah Rainsberger <sarah@rainsberger.ca>

.changeset/bright-feet-flash.md

@@ -0,0 +1,5 @@
+---
+'astro': minor
+---
+
+Adds a `'load'` prefetch strategy to prefetch links on page load

.changeset/two-hats-arrive.md

@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Ignores `3g` in slow connection detection. Only `2g` and `slow-2g` are considered slow connections.

packages/astro/e2e/fixtures/prefetch/src/pages/index.astro

@@ -20,6 +20,8 @@
     <span>Scroll down to trigger viewport prefetch</span>
     <!-- Large empty space to test viewport -->
     <div style="height: 1000px;"></div>
+    <a id="prefetch-load" href="/prefetch-load" data-astro-prefetch="load">load</a>
+    <br>
     <a id="prefetch-viewport" href="/prefetch-viewport" data-astro-prefetch="viewport">viewport</a>
     <script>
       // @ts-nocheck
@@ -29,4 +31,4 @@
       })
     </script>
   </body>
-</html>
+</html>

packages/astro/e2e/fixtures/prefetch/src/pages/prefetch-all.astro

@@ -0,0 +1 @@
+<h1>Prefetch load</h1>

packages/astro/e2e/prefetch.test.js

@@ -95,6 +95,12 @@ test.describe('Prefetch (default)', () => {
 		await page.locator('#prefetch-manual').click();
 		expect(reqUrls.filter((u) => u.includes('/prefetch-manual')).length).toEqual(1);
 	});
+
+	test('data-astro-prefetch="load" should prefetch', async ({ page, astro }) => {
+		await page.goto(astro.resolveUrl('/'));
+		expect(reqUrls).toContainEqual('/prefetch-load');
+		expect(page.locator('link[rel="prefetch"][href$="/prefetch-load"]')).toBeDefined();
+	});
 });
 
 test.describe("Prefetch (prefetchAll: true, defaultStrategy: 'tap')", () => {
@@ -182,4 +188,99 @@ test.describe("Prefetch (prefetchAll: true, defaultStrategy: 'tap')", () => {
 		expect(reqUrls).toContainEqual('/prefetch-viewport');
 		expect(page.locator('link[rel="prefetch"][href$="/prefetch-viewport"]')).toBeDefined();
 	});
+
+	test('data-astro-prefetch="load" should prefetch', async ({ page, astro }) => {
+		await page.goto(astro.resolveUrl('/'));
+		expect(reqUrls).toContainEqual('/prefetch-load');
+		expect(page.locator('link[rel="prefetch"][href$="/prefetch-load"]')).toBeDefined();
+	});
+});
+
+test.describe("Prefetch (prefetchAll: true, defaultStrategy: 'load')", () => {
+	let devServer;
+	/** @type {string[]} */
+	const reqUrls = [];
+
+	test.beforeAll(async ({ astro }) => {
+		devServer = await astro.startDevServer({
+			prefetch: {
+				prefetchAll: true,
+				defaultStrategy: 'load',
+			},
+		});
+	});
+
+	test.beforeEach(async ({ page }) => {
+		page.on('request', (req) => {
+			const urlObj = new URL(req.url());
+			reqUrls.push(urlObj.pathname + urlObj.search);
+		});
+	});
+
+	test.afterEach(() => {
+		reqUrls.length = 0;
+	});
+
+	test.afterAll(async () => {
+		await devServer.stop();
+	});
+
+	test('Link without data-astro-prefetch should prefetch', async ({ page, astro }) => {
+		await page.goto(astro.resolveUrl('/'));
+		expect(reqUrls).toContainEqual('/prefetch-default');
+		expect(page.locator('link[rel="prefetch"][href$="/prefetch-default"]')).toBeDefined();
+	});
+
+	test('data-astro-prefetch="false" should not prefetch', async ({ page, astro }) => {
+		await page.goto(astro.resolveUrl('/'));
+		expect(reqUrls).not.toContainEqual('/prefetch-false');
+	});
+
+	test('Link with search param should prefetch', async ({ page, astro }) => {
+		await page.goto(astro.resolveUrl('/'));
+		expect(reqUrls).not.toContainEqual('/?search-param=true');
+		await Promise.all([
+			page.waitForEvent('request'), // wait prefetch request
+			page.locator('#prefetch-search-param').hover(),
+		]);
+		expect(reqUrls).toContainEqual('/?search-param=true');
+	});
+
+	test('data-astro-prefetch="tap" should prefetch on tap', async ({ page, astro }) => {
+		await page.goto(astro.resolveUrl('/'));
+		expect(reqUrls).not.toContainEqual('/prefetch-tap');
+		await Promise.all([
+			page.waitForEvent('request'), // wait prefetch request
+			page.locator('#prefetch-tap').click(),
+		]);
+		expect(reqUrls).toContainEqual('/prefetch-tap');
+	});
+
+	test('data-astro-prefetch="hover" should prefetch on hover', async ({ page, astro }) => {
+		await page.goto(astro.resolveUrl('/'));
+		expect(reqUrls).not.toContainEqual('/prefetch-hover');
+		await Promise.all([
+			page.waitForEvent('request'), // wait prefetch request
+			page.locator('#prefetch-hover').hover(),
+		]);
+		expect(reqUrls).toContainEqual('/prefetch-hover');
+	});
+
+	test('data-astro-prefetch="viewport" should prefetch on viewport', async ({ page, astro }) => {
+		await page.goto(astro.resolveUrl('/'));
+		expect(reqUrls).not.toContainEqual('/prefetch-viewport');
+		// Scroll down to show the element
+		await Promise.all([
+			page.waitForEvent('request'), // wait prefetch request
+			page.locator('#prefetch-viewport').scrollIntoViewIfNeeded(),
+		]);
+		expect(reqUrls).toContainEqual('/prefetch-viewport');
+		expect(page.locator('link[rel="prefetch"][href$="/prefetch-viewport"]')).toBeDefined();
+	});
+
+	test('data-astro-prefetch="load" should prefetch', async ({ page, astro }) => {
+		await page.goto(astro.resolveUrl('/'));
+		expect(reqUrls).toContainEqual('/prefetch-load');
+		expect(page.locator('link[rel="prefetch"][href$="/prefetch-load"]')).toBeDefined();
+	});
 });

packages/astro/src/@types/astro.ts

@@ -949,22 +949,23 @@ export interface AstroUserConfig {
 				/**
 				 * @docs
 				 * @name prefetch.defaultStrategy
-				 * @type {'tap' | 'hover' | 'viewport'}
+				 * @type {'tap' | 'hover' | 'viewport' | 'load'}
 				 * @default `'hover'`
 				 * @description
 				 * The default prefetch strategy to use when the `data-astro-prefetch` attribute is set on a link with no value.
 				 *
 				 * - `'tap'`: Prefetch just before you click on the link.
 				 * - `'hover'`: Prefetch when you hover over or focus on the link. (default)
 				 * - `'viewport'`: Prefetch as the links enter the viewport.
+				 * - `'load'`: Prefetch the link without any restrictions.
 				 *
 				 * You can override this default value and select a different strategy for any individual link by setting a value on the attribute.
 				 *
 				 * ```html
 				 * <a href="/about" data-astro-prefetch="viewport">About</a>
 				 * ```
 				 */
-				defaultStrategy?: 'tap' | 'hover' | 'viewport';
+				defaultStrategy?: 'tap' | 'hover' | 'viewport' | 'load';
 		  };
 
 	/**

packages/astro/src/core/config/schema.ts

@@ -185,7 +185,7 @@ export const AstroConfigSchema = z.object({
 			z.boolean(),
 			z.object({
 				prefetchAll: z.boolean().optional(),
-				defaultStrategy: z.enum(['tap', 'hover', 'viewport']).optional(),
+				defaultStrategy: z.enum(['tap', 'hover', 'viewport', 'load']).optional(),
 			}),
 		])
 		.optional(),

packages/astro/src/prefetch/index.ts

@@ -45,6 +45,7 @@ export function init(defaultOpts?: InitOptions) {
 	initTapStrategy();
 	initHoverStrategy();
 	initViewportStrategy();
+	initLoadStrategy();
 }
 
 /**
@@ -169,6 +170,20 @@ function createViewportIntersectionObserver() {
 	});
 }
 
+/**
+ * Prefetch links with lower priority when page load
+ */
+function initLoadStrategy() {
+	onPageLoad(() => {
+		for (const anchor of document.getElementsByTagName('a')) {
+			if (elMatchesStrategy(anchor, 'load')) {
+				// Prefetch every link in this page
+				prefetch(anchor.href, { with: 'link' });
+			}
+		}
+	});
+}
+
 export interface PrefetchOptions {
 	/**
 	 * How the prefetch should prioritize the URL. (default `'link'`)
@@ -265,7 +280,7 @@ function isSlowConnection() {
 	if ('connection' in navigator) {
 		// Untyped Chrome-only feature: https://developer.mozilla.org/en-US/docs/Web/API/Navigator/connection
 		const conn = navigator.connection as any;
-		return conn.saveData || /(2|3)g/.test(conn.effectiveType);
+		return conn.saveData || /2g/.test(conn.effectiveType);
 	}
 	return false;
 }