Add router with region-based client-side navigation

packages/interactivity/src/index.js

@@ -2,20 +2,17 @@
  * Internal dependencies
  */
 import registerDirectives from './directives';
-import { init } from './hydration';
+import { init } from './router';
 import { rawStore, afterLoads } from './store';
 export { store } from './store';
 export { directive } from './hooks';
+export { navigate, prefetch } from './router';
 export { h as createElement } from 'preact';
 export { useEffect, useContext, useMemo } from 'preact/hooks';
 export { deepSignal } from 'deepsignal';
 
-/**
- * Initialize the Interactivity API.
- */
-registerDirectives();
-
 document.addEventListener( 'DOMContentLoaded', async () => {
+	registerDirectives();
 	await init();
 	afterLoads.forEach( ( afterLoad ) => afterLoad( rawStore ) );
 } );

packages/interactivity/src/router.js

@@ -0,0 +1,127 @@
+/**
+ * External dependencies
+ */
+import { hydrate, render } from 'preact';
+/**
+ * Internal dependencies
+ */
+import { toVdom, hydratedIslands } from './vdom';
+import { createRootFragment } from './utils';
+import { directivePrefix } from './constants';
+
+// The cache of visited and prefetched pages.
+const pages = new Map();
+
+// Keep the same root fragment for each interactive region node.
+const regionRootFragments = new WeakMap();
+const getRegionRootFragment = ( region ) => {
+	if ( ! regionRootFragments.has( region ) ) {
+		regionRootFragments.set(
+			region,
+			createRootFragment( region.parentElement, region )
+		);
+	}
+	return regionRootFragments.get( region );
+};
+
+// Helper to remove domain and hash from the URL. We are only interesting in
+// caching the path and the query.
+const cleanUrl = ( url ) => {
+	const u = new URL( url, window.location );
+	return u.pathname + u.search;
+};
+
+// Fetch a new page and convert it to a static virtual DOM.
+const fetchPage = async ( url, { html } ) => {
+	try {
+		if ( ! html ) {
+			const res = await window.fetch( url );
+			if ( res.status !== 200 ) return false;
+			html = await res.text();
+		}
+		const dom = new window.DOMParser().parseFromString( html, 'text/html' );
+		return regionsToVdom( dom );
+	} catch ( e ) {
+		return false;
+	}
+};
+
+// Return an object with VDOM trees of those HTML regions marked with a
+// `navigation-id` directive.
+const regionsToVdom = ( dom ) => {
+	const regions = {};
+	const attrName = `data-${ directivePrefix }-navigation-id`;
+	dom.querySelectorAll( `[${ attrName }]` ).forEach( ( region ) => {
+		const id = region.getAttribute( attrName );
+		regions[ id ] = toVdom( region );
+	} );
+
+	return { regions };
+};
+
+// Prefetch a page. We store the promise to avoid triggering a second fetch for
+// a page if a fetching has already started.
+export const prefetch = ( url, options = {} ) => {
+	url = cleanUrl( url );
+	if ( options.force || ! pages.has( url ) ) {
+		pages.set( url, fetchPage( url, options ) );
+	}
+};
+
+// Render all interactive regions contained in the given page.
+const renderRegions = ( page ) => {
+	const attrName = `data-${ directivePrefix }-navigation-id`;
+	document.querySelectorAll( `[${ attrName }]` ).forEach( ( region ) => {
+		const id = region.getAttribute( attrName );
+		const fragment = getRegionRootFragment( region );
+		render( page.regions[ id ], fragment );
+	} );
+};
+
+// Navigate to a new page.
+export const navigate = async ( href, options = {} ) => {
+	const url = cleanUrl( href );
+	prefetch( url, options );
+	const page = await pages.get( url );
+	if ( page ) {
+		renderRegions( page );
+		window.history[ options.replace ? 'replaceState' : 'pushState' ](
+			{},
+			'',
+			href
+		);
+	} else {
+		window.location.assign( href );
+	}
+};
+
+// Listen to the back and forward buttons and restore the page if it's in the
+// cache.
+window.addEventListener( 'popstate', async () => {
+	const url = cleanUrl( window.location ); // Remove hash.
+	const page = pages.has( url ) && ( await pages.get( url ) );
+	if ( page ) {
+		renderRegions( page );
+	} else {
+		window.location.reload();
+	}
+} );
+
+// Initialize the router with the initial DOM.
+export const init = async () => {
+	document
+		.querySelectorAll( `[data-${ directivePrefix }-interactive]` )
+		.forEach( ( node ) => {
+			if ( ! hydratedIslands.has( node ) ) {
+				const fragment = getRegionRootFragment( node );
+				const vdom = toVdom( node );
+				hydrate( vdom, fragment );
+			}
+		} );
+
+	// Cache the current regions.
+	pages.set(
+		cleanUrl( window.location ),
+		Promise.resolve( regionsToVdom( document ) )
+	);
+};