implement no scroll state

src/runtime/index.ts

@@ -292,16 +292,17 @@ function prepare_page(target: Target): Promise<{
 	});
 }
 
-async function navigate(target: Target, id: number): Promise<any> {
+async function navigate(target: Target, id: number, noscroll = false): Promise<any> {
 	if (id) {
 		// popstate or initial navigation
 		cid = id;
 	} else {
 		// clicked on a link. preserve scroll state
-		scroll_history[cid] = scroll_state();
+		const scrollState = scroll_state()
+		scroll_history[cid] = scrollState;
 
 		id = cid = ++uid;
-		scroll_history[cid] = { x: 0, y: 0 };
+		scroll_history[cid] = noscroll ? scrollState : { x: 0, y: 0 };
 	}
 
 	cid = id;
@@ -362,8 +363,9 @@ function handle_click(event: MouseEvent) {
 	if (url.pathname === window.location.pathname && url.search === window.location.search) return;
 
 	const target = select_route(url);
+	const hasNoscroll = a.hasAttribute('sapper-noscroll')
 	if (target) {
-		navigate(target, null);
+		navigate(target, null, hasNoscroll);
 		event.preventDefault();
 		history.pushState({ id: cid }, '', url.href);
 	}