feat(nuxt): default router scroll behavior (#3851)

Co-authored-by: joel <joel.wenzel@flexagon.com>
Co-authored-by: Pooya Parsa <pooya@pi0.io>

docs/content/3.api/4.advanced/1.hooks.md

@@ -27,6 +27,7 @@ Hook                   | Arguments           | Environment     | Description
 `link:prefetch`        | `to`                | Client          | Called when a `<NuxtLink>` is observed to be prefetched.
 `page:start`           | `pageComponent?`    | Client          | Called on [Suspense](https://vuejs.org/guide/built-ins/suspense.html#suspense) pending event.
 `page:finish`          | `pageComponent?`    | Client          | Called on [Suspense](https://vuejs.org/guide/built-ins/suspense.html#suspense) resolved event.
+`page:transition:finish`| `pageComponent?`    | Client          | After page transition [onAfterLeave](https://vuejs.org/guide/built-ins/transition.html#javascript-hooks) event.
 
 # Nuxt Hooks (build time)
 

packages/nuxt/src/app/nuxt.ts

@@ -34,6 +34,7 @@ export interface RuntimeNuxtHooks {
   'link:prefetch': (link: string) => HookResult
   'page:start': (Component?: VNode) => HookResult
   'page:finish': (Component?: VNode) => HookResult
+  'page:transition:finish': (Component?: VNode) => HookResult
   'vue:setup': () => void
   'vue:error': (...args: Parameters<Parameters<typeof onErrorCaptured>[0]>) => HookResult
 }

packages/nuxt/src/pages/module.ts

@@ -139,11 +139,14 @@ export default defineNuxtModule({
     addTemplate({
       filename: 'router.options.mjs',
       getContents: async () => {
-        // Check for router options
+        // Scan and register app/router.options files
         const routerOptionsFiles = (await Promise.all(nuxt.options._layers.map(
           async layer => await findPath(resolve(layer.config.srcDir, 'app/router.options'))
         ))).filter(Boolean) as string[]
 
+        // Add default options
+        routerOptionsFiles.unshift(resolve(runtimeDir, 'router.options'))
+
         const configRouterOptions = genObjectFromRawEntries(Object.entries(nuxt.options.router.options)
           .map(([key, value]) => [key, genString(value as string)]))
 

packages/nuxt/src/pages/runtime/composables.ts

@@ -29,6 +29,8 @@ export interface PageMeta {
   layoutTransition?: boolean | TransitionProps
   key?: false | string | ((route: RouteLocationNormalizedLoaded) => string)
   keepalive?: boolean | KeepAliveProps
+  /** Set to `false` to avoid scrolling to top on page navigations */
+  scrollToTop?: boolean
 }
 
 declare module 'vue-router' {

packages/nuxt/src/pages/runtime/page.ts

@@ -1,6 +1,7 @@
 import { computed, defineComponent, h, provide, reactive, onMounted, nextTick, Suspense, Transition, KeepAliveProps, TransitionProps } from 'vue'
 import type { DefineComponent, VNode } from 'vue'
 import { RouterView } from 'vue-router'
+import { defu } from 'defu'
 import type { RouteLocationNormalized, RouteLocationNormalizedLoaded, RouteLocation } from 'vue-router'
 
 import { generateRouteKey, RouterViewSlotProps, wrapInKeepAlive } from './utils'
@@ -34,22 +35,27 @@ export default defineComponent({
   },
   setup (props, { attrs }) {
     const nuxtApp = useNuxtApp()
-
     return () => {
       return h(RouterView, { name: props.name, route: props.route, ...attrs }, {
         default: (routeProps: RouterViewSlotProps) => {
           if (!routeProps.Component) { return }
 
           const key = generateRouteKey(props.pageKey, routeProps)
-          const transitionProps = props.transition ?? routeProps.route.meta.pageTransition ?? (defaultPageTransition as TransitionProps)
-
           const done = nuxtApp.deferHydration()
 
-          return _wrapIf(Transition, transitionProps,
+          const hasTransition = !!(props.transition ?? routeProps.route.meta.pageTransition ?? defaultPageTransition)
+          const transitionProps = hasTransition && _mergeTransitionProps([
+            props.transition,
+            routeProps.route.meta.pageTransition,
+            defaultPageTransition,
+            { onAfterLeave: () => { nuxtApp.callHook('page:transition:finish', routeProps.Component) } }
+          ].filter(Boolean))
+
+          return _wrapIf(Transition, hasTransition && transitionProps,
             wrapInKeepAlive(props.keepalive ?? routeProps.route.meta.keepalive ?? (defaultKeepaliveConfig as KeepAliveProps), h(Suspense, {
               onPending: () => nuxtApp.callHook('page:start', routeProps.Component),
-              onResolve: () => nuxtApp.callHook('page:finish', routeProps.Component).finally(done)
-            }, { default: () => h(Component, { key, routeProps, pageKey: key, hasTransition: !!transitionProps } as {}) })
+              onResolve: () => { nextTick(() => nuxtApp.callHook('page:finish', routeProps.Component).finally(done)) }
+            }, { default: () => h(Component, { key, routeProps, pageKey: key, hasTransition } as {}) })
             )).default()
         }
       })
@@ -62,6 +68,19 @@ export default defineComponent({
   [key: string]: any
 }>
 
+function _toArray (val: any) {
+  return Array.isArray(val) ? val : (val ? [val] : [])
+}
+
+function _mergeTransitionProps (routeProps: TransitionProps[]): TransitionProps {
+  const _props: TransitionProps[] = routeProps.map(prop => ({
+    ...prop,
+    onAfterLeave: _toArray(prop.onAfterLeave)
+  }))
+  // @ts-ignore
+  return defu(..._props)
+}
+
 const Component = defineComponent({
   // TODO: Type props
   // eslint-disable-next-line vue/require-prop-types

packages/nuxt/src/pages/runtime/router.options.ts

@@ -0,0 +1,58 @@
+import type { RouterConfig } from '@nuxt/schema'
+import type { RouterScrollBehavior } from 'vue-router'
+import { nextTick } from 'vue'
+import { useNuxtApp } from '#app'
+
+type ScrollPosition = Awaited<ReturnType<RouterScrollBehavior>>
+
+// Default router options
+// https://router.vuejs.org/api/#routeroptions
+export default <RouterConfig> {
+  scrollBehavior (to, from, savedPosition) {
+    const nuxtApp = useNuxtApp()
+
+    // By default when the returned position is falsy or an empty object, vue-router will retain the current scroll position
+    // savedPosition is only available for popstate navigations (back button)
+    let position: ScrollPosition = savedPosition || undefined
+
+    // Scroll to top if route is changed by default
+    if (
+      !position &&
+      (from && to && from.matched[0] !== to.matched[0]) &&
+      to.meta.scrollToTop !== false
+    ) {
+      position = { left: 0, top: 0 }
+    }
+
+    // Hash routes on the same page, no page hook is fired so resolve here
+    if (to.path !== from.path) {
+      if (from.hash && !to.hash) {
+        return { left: 0, top: 0 }
+      }
+      if (to.hash) {
+        return { el: to.hash, top: _getHashElementScrollMarginTop(to.hash) }
+      }
+    }
+
+    // Wait for `page:transition:finish` or `page:finish` depending on if transitions are enabled or not
+    const hasTransition = to.meta.pageTransition !== false && from.meta.pageTransition !== false
+    const hookToWait = hasTransition ? 'page:transition:finish' : 'page:finish'
+    return new Promise((resolve) => {
+      nuxtApp.hooks.hookOnce(hookToWait, async () => {
+        await nextTick()
+        if (to.hash) {
+          position = { el: to.hash, top: _getHashElementScrollMarginTop(to.hash) }
+        }
+        resolve(position)
+      })
+    })
+  }
+}
+
+function _getHashElementScrollMarginTop (selector: string): number {
+  const elem = document.querySelector(selector)
+  if (elem) {
+    return parseFloat(getComputedStyle(elem).scrollMarginTop)
+  }
+  return 0
+}