diff --git a/__tests__/e2e/data-loading/data.test.ts b/__tests__/e2e/data-loading/data.test.ts
index fafc403acb9f..1eb267e3896c 100644
--- a/__tests__/e2e/data-loading/data.test.ts
+++ b/__tests__/e2e/data-loading/data.test.ts
@@ -54,7 +54,7 @@ describe('static data file support in vite 3', () => {
           document.querySelector('pre#basic')?.textContent ===
           JSON.stringify([{ a: false }, { b: true }], null, 2),
         undefined,
-        { timeout: 3000 }
+        { timeout: 5000 }
       )
     } finally {
       await fs.writeFile(a, JSON.stringify({ a: true }, null, 2) + '\n')
@@ -69,7 +69,7 @@ describe('static data file support in vite 3', () => {
           document.querySelector('pre#basic')?.textContent ===
           JSON.stringify([{ a: true }], null, 2),
         undefined,
-        { timeout: 3000 }
+        { timeout: 5000 }
       )
       err = false
     } finally {
@@ -85,7 +85,7 @@ describe('static data file support in vite 3', () => {
           document.querySelector('pre#basic')?.textContent ===
           JSON.stringify([{ a: true }, { b: false }], null, 2),
         undefined,
-        { timeout: 3000 }
+        { timeout: 5000 }
       )
     } finally {
       await fs.writeFile(b, JSON.stringify({ b: true }, null, 2) + '\n')
diff --git a/package.json b/package.json
index c3558638208f..c44921595ab3 100644
--- a/package.json
+++ b/package.json
@@ -107,6 +107,7 @@
     "@vueuse/core": "^13.1.0",
     "@vueuse/integrations": "^13.1.0",
     "focus-trap": "^7.6.4",
+    "living-object": "0.0.8",
     "mark.js": "8.11.1",
     "minisearch": "^7.1.2",
     "shiki": "^3.2.2",
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index d4c6d0c319f3..9b4dce596cb6 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -55,6 +55,9 @@ importers:
       focus-trap:
         specifier: ^7.6.4
         version: 7.6.4
+      living-object:
+        specifier: 0.0.8
+        version: 0.0.8
       mark.js:
         specifier: 8.11.1
         version: 8.11.1
@@ -1966,6 +1969,10 @@ packages:
     resolution: {integrity: sha512-vsBzcU4oE+v0lj4FhVLzr9dBTv4/fHIa57l+GCwovP8MoFNZJTOhGU8PXd4v2VJCbECAaijBiHntiekFMLvo0g==}
     engines: {node: '>=18.0.0'}
 
+  living-object@0.0.8:
+    resolution: {integrity: sha512-o4SGS1iyo3H6m/OAbrxty0RFgXNIkx0vojHDGcAk/RjQ+noB0lsK2znmq19BZ+jyOS7P0jj5zywxgVNuKt5/Gg==}
+    engines: {node: '>=16.0.0'}
+
   local-pkg@1.1.1:
     resolution: {integrity: sha512-WunYko2W1NcdfAFpuLUoucsgULmgDBRkdxHxWQ7mK0cQqwPiy8E1enjuRBrhLtZkB5iScJ1XIPdhVEFK8aOLSg==}
     engines: {node: '>=14'}
@@ -4677,6 +4684,8 @@ snapshots:
       rfdc: 1.4.1
       wrap-ansi: 9.0.0
 
+  living-object@0.0.8: {}
+
   local-pkg@1.1.1:
     dependencies:
       mlly: 1.7.4
diff --git a/src/client/app/components/ClientOnly.ts b/src/client/app/components/ClientOnly.ts
index 680094ce5807..1781a371263a 100644
--- a/src/client/app/components/ClientOnly.ts
+++ b/src/client/app/components/ClientOnly.ts
@@ -1,7 +1,17 @@
 import { defineComponent, onMounted, ref } from 'vue'
 
 export const ClientOnly = defineComponent({
-  setup(_, { slots }) {
+  props: {
+    isClientOnly: {
+      type: Boolean,
+      default: true
+    }
+  },
+  setup(props, { slots }) {
+    // Programmatically determine if this component should be
+    // client-only based on the presence of the isClientOnly attribute.
+    if (!props.isClientOnly) return () => slots.default?.(props) || null
+
     const show = ref(false)
 
     onMounted(() => {
diff --git a/src/client/theme-default/components/VPNavBarMenu.vue b/src/client/theme-default/components/VPNavBarMenu.vue
index c4d741b97a97..e15cc48936ec 100644
--- a/src/client/theme-default/components/VPNavBarMenu.vue
+++ b/src/client/theme-default/components/VPNavBarMenu.vue
@@ -2,29 +2,32 @@
 import { useData } from '../composables/data'
 import VPNavBarMenuLink from './VPNavBarMenuLink.vue'
 import VPNavBarMenuGroup from './VPNavBarMenuGroup.vue'
+import { isClientOnly } from '../../shared'
 
 const { theme } = useData()
 </script>
 
 <template>
-  <nav
-    v-if="theme.nav"
-    aria-labelledby="main-nav-aria-label"
-    class="VPNavBarMenu"
-  >
-    <span id="main-nav-aria-label" class="visually-hidden">
-      Main Navigation
-    </span>
-    <template v-for="item in theme.nav" :key="JSON.stringify(item)">
-      <VPNavBarMenuLink v-if="'link' in item" :item />
-      <component
-        v-else-if="'component' in item"
-        :is="item.component"
-        v-bind="item.props"
-      />
-      <VPNavBarMenuGroup v-else :item />
-    </template>
-  </nav>
+  <ClientOnly :is-client-only="isClientOnly(theme.nav)">
+    <nav
+      v-if="theme.nav"
+      aria-labelledby="main-nav-aria-label"
+      class="VPNavBarMenu"
+    >
+      <span id="main-nav-aria-label" class="visually-hidden">
+        Main Navigation
+      </span>
+      <template v-for="item in theme.nav" :key="JSON.stringify(item)">
+        <VPNavBarMenuLink v-if="'link' in item" :item />
+        <component
+          v-else-if="'component' in item"
+          :is="item.component"
+          v-bind="item.props"
+        />
+        <VPNavBarMenuGroup v-else :item />
+      </template>
+    </nav>
+  </ClientOnly>
 </template>
 
 <style scoped>
diff --git a/src/client/theme-default/components/VPSidebar.vue b/src/client/theme-default/components/VPSidebar.vue
index c2de0a0d8356..92f4f521ce00 100644
--- a/src/client/theme-default/components/VPSidebar.vue
+++ b/src/client/theme-default/components/VPSidebar.vue
@@ -5,7 +5,7 @@ import { ref, watch } from 'vue'
 import { useLayout } from '../composables/layout'
 import VPSidebarGroup from './VPSidebarGroup.vue'
 
-const { sidebarGroups, hasSidebar } = useLayout()
+const { sidebarGroups, hasSidebar, isSidebarClientOnly } = useLayout()
 
 const props = defineProps<{
   open: boolean
@@ -38,27 +38,18 @@ watch(
 </script>
 
 <template>
-  <aside
-    v-if="hasSidebar"
-    class="VPSidebar"
-    :class="{ open }"
-    ref="navEl"
-    @click.stop
-  >
+  <aside v-if="hasSidebar" class="VPSidebar" :class="{ open }" ref="navEl" @click.stop>
     <div class="curtain" />
 
-    <nav
-      class="nav"
-      id="VPSidebarNav"
-      aria-labelledby="sidebar-aria-label"
-      tabindex="-1"
-    >
+    <nav class="nav" id="VPSidebarNav" aria-labelledby="sidebar-aria-label" tabindex="-1">
       <span class="visually-hidden" id="sidebar-aria-label">
         Sidebar Navigation
       </span>
 
       <slot name="sidebar-nav-before" />
-      <VPSidebarGroup :items="sidebarGroups" :key />
+      <ClientOnly :is-client-only="isSidebarClientOnly">
+        <VPSidebarGroup :items="sidebarGroups" :key />
+      </ClientOnly>
       <slot name="sidebar-nav-after" />
     </nav>
   </aside>
diff --git a/src/client/theme-default/components/VPSidebarGroup.vue b/src/client/theme-default/components/VPSidebarGroup.vue
index 0c20017416c3..e7552c873ca4 100644
--- a/src/client/theme-default/components/VPSidebarGroup.vue
+++ b/src/client/theme-default/components/VPSidebarGroup.vue
@@ -2,6 +2,7 @@
 import type { DefaultTheme } from 'vitepress/theme'
 import { onBeforeUnmount, onMounted, ref } from 'vue'
 import VPSidebarItem from './VPSidebarItem.vue'
+import { isClientOnly } from '../../shared'
 
 defineProps<{
   items: DefaultTheme.SidebarItem[]
@@ -33,7 +34,9 @@ onBeforeUnmount(() => {
     class="group"
     :class="{ 'no-transition': disableTransition }"
   >
-    <VPSidebarItem :item :depth="0" />
+    <ClientOnly :is-client-only="isClientOnly(item)">
+      <VPSidebarItem :item :depth="0" />
+    </ClientOnly>
   </div>
 </template>
 
diff --git a/src/client/theme-default/components/VPSidebarItem.vue b/src/client/theme-default/components/VPSidebarItem.vue
index d71d10621dcd..fe481a95f8e6 100644
--- a/src/client/theme-default/components/VPSidebarItem.vue
+++ b/src/client/theme-default/components/VPSidebarItem.vue
@@ -3,6 +3,7 @@ import type { DefaultTheme } from 'vitepress/theme'
 import { computed } from 'vue'
 import { useSidebarItemControl } from '../composables/sidebar'
 import VPLink from './VPLink.vue'
+import { isClientOnly } from '../../shared'
 
 const props = defineProps<{
   item: DefaultTheme.SidebarItem
@@ -55,56 +56,58 @@ function onCaretClick() {
 </script>
 
 <template>
-  <component :is="sectionTag" class="VPSidebarItem" :class="classes">
-    <div
-      v-if="item.text"
-      class="item"
-      :role="itemRole"
-      v-on="
-        item.items
-          ? { click: onItemInteraction, keydown: onItemInteraction }
-          : {}
-      "
-      :tabindex="item.items && 0"
-    >
-      <div class="indicator" />
-
-      <VPLink
-        v-if="item.link"
-        :tag="linkTag"
-        class="link"
-        :href="item.link"
-        :rel="item.rel"
-        :target="item.target"
-      >
-        <component :is="textTag" class="text" v-html="item.text" />
-      </VPLink>
-      <component v-else :is="textTag" class="text" v-html="item.text" />
-
+  <ClientOnly :is-client-only="isClientOnly(item)">
+    <component :is="sectionTag" class="VPSidebarItem" :class="classes">
       <div
-        v-if="item.collapsed != null && item.items && item.items.length"
-        class="caret"
-        role="button"
-        aria-label="toggle section"
-        @click="onCaretClick"
-        @keydown.enter="onCaretClick"
-        tabindex="0"
+        v-if="item.text"
+        class="item"
+        :role="itemRole"
+        v-on="
+          item.items
+            ? { click: onItemInteraction, keydown: onItemInteraction }
+            : {}
+        "
+        :tabindex="item.items && 0"
       >
-        <span class="vpi-chevron-right caret-icon" />
+        <div class="indicator" />
+
+        <VPLink
+          v-if="item.link"
+          :tag="linkTag"
+          class="link"
+          :href="item.link"
+          :rel="item.rel"
+          :target="item.target"
+        >
+          <component :is="textTag" class="text" v-html="item.text" />
+        </VPLink>
+        <component v-else :is="textTag" class="text" v-html="item.text" />
+
+        <div
+          v-if="item.collapsed != null && item.items && item.items.length"
+          class="caret"
+          role="button"
+          aria-label="toggle section"
+          @click="onCaretClick"
+          @keydown.enter="onCaretClick"
+          tabindex="0"
+        >
+          <span class="vpi-chevron-right caret-icon" />
+        </div>
+      </div>
+
+      <div v-if="item.items && item.items.length" class="items">
+        <template v-if="depth < 5">
+          <VPSidebarItem
+            v-for="i in item.items"
+            :key="i.text"
+            :item="i"
+            :depth="depth + 1"
+          />
+        </template>
       </div>
-    </div>
-
-    <div v-if="item.items && item.items.length" class="items">
-      <template v-if="depth < 5">
-        <VPSidebarItem
-          v-for="i in item.items"
-          :key="i.text"
-          :item="i"
-          :depth="depth + 1"
-        />
-      </template>
-    </div>
-  </component>
+    </component>
+  </ClientOnly>
 </template>
 
 <style scoped>
diff --git a/src/client/theme-default/composables/layout.ts b/src/client/theme-default/composables/layout.ts
index 1b993ea65c17..01c729d20fb3 100644
--- a/src/client/theme-default/composables/layout.ts
+++ b/src/client/theme-default/composables/layout.ts
@@ -5,6 +5,7 @@ import { getSidebar, getSidebarGroups } from '../support/sidebar'
 import { useData } from './data'
 import { getHeaders } from './outline'
 import { useCloseSidebarOnEscape } from './sidebar'
+import { isClientOnly } from '../../shared'
 
 const headers = shallowRef<DefaultTheme.OutlineItem[]>([])
 const sidebar = shallowRef<DefaultTheme.SidebarItem[]>([])
@@ -28,6 +29,10 @@ export function useLayout(): ReturnType<typeof expected> {
 
   const isSidebarEnabled = computed(() => hasSidebar.value && is960.value)
 
+  const isSidebarClientOnly = computed(
+    () => isClientOnly(theme.value.sidebar) || isClientOnly(sidebar.value)
+  )
+
   const sidebarGroups = computed(() => {
     return hasSidebar.value ? getSidebarGroups(sidebar.value) : []
   })
@@ -55,6 +60,7 @@ export function useLayout(): ReturnType<typeof expected> {
     sidebarGroups,
     hasSidebar,
     isSidebarEnabled,
+    isSidebarClientOnly,
     hasAside,
     leftAside,
     headers: shallowReadonly(headers),
diff --git a/src/client/theme-default/support/sidebar.ts b/src/client/theme-default/support/sidebar.ts
index 201f2536412b..e2afc591e433 100644
--- a/src/client/theme-default/support/sidebar.ts
+++ b/src/client/theme-default/support/sidebar.ts
@@ -1,5 +1,5 @@
 import type { DefaultTheme } from 'vitepress/theme'
-import { isActive } from '../../shared'
+import { isActive, propagateClientOnly } from '../../shared'
 import { ensureStartingSlash } from './utils'
 
 export interface SidebarLink {
@@ -108,12 +108,13 @@ export function hasActiveLink(
       : false
 }
 
-function addBase(items: SidebarItem[], _base?: string): SidebarItem[] {
-  return [...items].map((_item) => {
+function addBase(items: SidebarItem[], _base?: string) {
+  const result = [...items].map((_item) => {
     const item = { ..._item }
     const base = item.base || _base
     if (base && item.link) item.link = base + item.link
     if (item.items) item.items = addBase(item.items, base)
-    return item
+    return propagateClientOnly(item, _item)
   })
+  return propagateClientOnly(items, result)
 }
diff --git a/src/node/build/build.ts b/src/node/build/build.ts
index a0a12610de83..44d3aa045953 100644
--- a/src/node/build/build.ts
+++ b/src/node/build/build.ts
@@ -11,11 +11,11 @@ import type { BuildOptions, Rollup } from 'vite'
 import { resolveConfig, type SiteConfig } from '../config'
 import { clearCache } from '../markdownToVue'
 import { slash, type Awaitable, type HeadConfig } from '../shared'
-import { deserializeFunctions, serializeFunctions } from '../utils/fnSerialize'
 import { task } from '../utils/task'
 import { bundle } from './bundle'
 import { generateSitemap } from './generateSitemap'
 import { renderPage } from './render'
+import LivingObject from 'living-object'
 
 const require = createRequire(import.meta.url)
 
@@ -202,15 +202,11 @@ function generateMetadataScript(
   // It's also embedded as a string and JSON.parsed from the client because
   // it's faster than embedding as JS object literal.
   const hashMapString = JSON.stringify(JSON.stringify(pageToHashMap))
-  const siteDataString = JSON.stringify(
-    JSON.stringify(serializeFunctions({ ...config.site, head: [] }))
-  )
+  const siteDataString = new LivingObject({ ...config.site, head: [] })
+    .compile()
+    .complete((root) => `window.__VP_SITE_DATA__=${root}`)
 
-  const metadataContent = `window.__VP_HASH_MAP__=JSON.parse(${hashMapString});${
-    siteDataString.includes('_vp-fn_')
-      ? `${deserializeFunctions};window.__VP_SITE_DATA__=deserializeFunctions(JSON.parse(${siteDataString}));`
-      : `window.__VP_SITE_DATA__=JSON.parse(${siteDataString});`
-  }`
+  const metadataContent = `{window.__VP_HASH_MAP__=JSON.parse(${hashMapString});${siteDataString};}`
 
   if (!config.metaChunk) {
     return { html: `<script>${metadataContent}</script>`, inHead: false }
diff --git a/src/node/config.ts b/src/node/config.ts
index 959e39bd761e..cee15ed8d3cd 100644
--- a/src/node/config.ts
+++ b/src/node/config.ts
@@ -15,7 +15,7 @@ import type { DefaultTheme } from './defaultTheme'
 import { resolvePages } from './plugins/dynamicRoutesPlugin'
 import {
   APPEARANCE_KEY,
-  VP_SOURCE_KEY,
+  VP_CONFIG_SOURCE,
   isObject,
   slash,
   type AdditionalConfig,
@@ -28,6 +28,7 @@ import type { RawConfigExports, SiteConfig, UserConfig } from './siteConfig'
 export { resolvePages } from './plugins/dynamicRoutesPlugin'
 export { resolveSiteDataByRoute } from './shared'
 export * from './siteConfig'
+export { clientOnly, isClientOnly } from './shared'
 
 const debug = _debug('vitepress:config')
 
@@ -218,7 +219,7 @@ async function gatherAdditionalConfig(
       )
 
       if (mode === 'development') {
-        ;(configExports.config as any)[VP_SOURCE_KEY] = '/' + slash(file)
+        ;(configExports.config as any)[VP_CONFIG_SOURCE] = '/' + slash(file)
       }
 
       return [id, configExports.config as AdditionalConfig] as const
diff --git a/src/node/plugin.ts b/src/node/plugin.ts
index f6c3d3f98ea0..2b176bf160cf 100644
--- a/src/node/plugin.ts
+++ b/src/node/plugin.ts
@@ -33,7 +33,7 @@ import { rewritesPlugin } from './plugins/rewritesPlugin'
 import { staticDataPlugin } from './plugins/staticDataPlugin'
 import { webFontsPlugin } from './plugins/webFontsPlugin'
 import { slash, type PageDataPayload } from './shared'
-import { deserializeFunctions, serializeFunctions } from './utils/fnSerialize'
+import { stringify as serializeSiteData } from 'living-object'
 
 declare module 'vite' {
   interface UserConfig {
@@ -203,8 +203,7 @@ export async function createVitePressPlugin(
             return `export default window.__VP_SITE_DATA__`
           }
         }
-        data = serializeFunctions(data)
-        return `${deserializeFunctions};export default deserializeFunctions(JSON.parse(${JSON.stringify(JSON.stringify(data))}))`
+        return serializeSiteData(data, { target: 'module' })
       }
     },
 
diff --git a/src/node/utils/fnSerialize.ts b/src/node/utils/fnSerialize.ts
deleted file mode 100644
index 242ca90d3a33..000000000000
--- a/src/node/utils/fnSerialize.ts
+++ /dev/null
@@ -1,42 +0,0 @@
-export function serializeFunctions(value: any, key?: string): any {
-  if (Array.isArray(value)) {
-    return value.map((v) => serializeFunctions(v))
-  } else if (typeof value === 'object' && value !== null) {
-    return Object.keys(value).reduce((acc, key) => {
-      if (key[0] === '_') return acc
-      acc[key] = serializeFunctions(value[key], key)
-      return acc
-    }, {} as any)
-  } else if (typeof value === 'function') {
-    let serialized = value.toString()
-    if (
-      key &&
-      (serialized.startsWith(key) || serialized.startsWith('async ' + key))
-    ) {
-      serialized = serialized.replace(key, 'function')
-    }
-    return `_vp-fn_${serialized}`
-  } else {
-    return value
-  }
-}
-
-/*
-export function deserializeFunctions(value: any): any {
-  if (Array.isArray(value)) {
-    return value.map(deserializeFunctions)
-  } else if (typeof value === 'object' && value !== null) {
-    return Object.keys(value).reduce((acc, key) => {
-      acc[key] = deserializeFunctions(value[key])
-      return acc
-    }, {} as any)
-  } else if (typeof value === 'string' && value.startsWith('_vp-fn_')) {
-    return new Function(`return ${value.slice(7)}`)()
-  } else {
-    return value
-  }
-}
-*/
-
-export const deserializeFunctions =
-  'function deserializeFunctions(r){return Array.isArray(r)?r.map(deserializeFunctions):typeof r=="object"&&r!==null?Object.keys(r).reduce((t,n)=>(t[n]=deserializeFunctions(r[n]),t),{}):typeof r=="string"&&r.startsWith("_vp-fn_")?new Function(`return ${r.slice(7)}`)():r}'
diff --git a/src/shared/shared.ts b/src/shared/shared.ts
index 3caca9a92189..5c047e1c01f6 100644
--- a/src/shared/shared.ts
+++ b/src/shared/shared.ts
@@ -25,7 +25,11 @@ export type {
 export const EXTERNAL_URL_RE = /^(?:[a-z]+:|\/\/)/i
 export const APPEARANCE_KEY = 'vitepress-theme-appearance'
 
-export const VP_SOURCE_KEY = '[VP_SOURCE]'
+// Global symbols will be preserved by living-object.
+export const VP_CONFIG_SOURCE = Symbol.for('VP:ConfigSource')
+export const VP_CLIENT_ONLY = Symbol.for('VP:ClientOnly')
+// Private symbols are distinct in each runtime environment.
+// This should only be used internally.
 const UnpackStackView = Symbol('stack-view:unpack')
 
 const HASH_RE = /#.*$/
@@ -111,7 +115,7 @@ export function resolveSiteDataByRoute(
   const additionalConfigs = resolveAdditionalConfig(siteData, relativePath)
 
   if (inBrowser && (import.meta as any).env?.DEV) {
-    ;(localeConfig as any)[VP_SOURCE_KEY] = `locale config (${localeIndex})`
+    ;(localeConfig as any)[VP_CONFIG_SOURCE] = `locale config (${localeIndex})`
     reportConfigLayers(relativePath, [
       ...additionalConfigs,
       localeConfig,
@@ -296,7 +300,7 @@ function reportConfigLayers(path: string, layers: Partial<SiteData>[]) {
   const summary = layers.map((c, i, arr) => {
     const n = i + 1
     if (n === arr.length) return `${n}. .vitepress/config (root)`
-    return `${n}. ${(c as any)?.[VP_SOURCE_KEY] ?? '(Unknown Source)'}`
+    return `${n}. ${(c as any)?.[VP_CONFIG_SOURCE] ?? '(Unknown Source)'}`
   })
 
   console.debug(
@@ -352,3 +356,19 @@ type ObjectType = Record<PropertyKey, any>
 export function isObject(value: unknown): value is ObjectType {
   return Object.prototype.toString.call(value) === '[object Object]'
 }
+
+export function clientOnly<T extends object>(object: T) {
+  ;(object as any)[VP_CLIENT_ONLY] = true
+  return object
+}
+
+export function isClientOnly<T extends object>(object?: T): boolean {
+  return (object as any)?.[VP_CLIENT_ONLY] ?? false
+}
+
+export function propagateClientOnly<T extends object>(src: T, dst: T): T {
+  if (isClientOnly(src)) {
+    clientOnly(dst)
+  }
+  return dst
+}
diff --git a/theme.d.ts b/theme.d.ts
index 9d6664003a52..fcf4c2c80d9d 100644
--- a/theme.d.ts
+++ b/theme.d.ts
@@ -20,6 +20,7 @@ export declare const useLayout: () => {
   sidebarGroups: ComputedRef<DefaultTheme.SidebarItem[]>
   hasSidebar: ComputedRef<boolean>
   isSidebarEnabled: ComputedRef<boolean>
+  isSidebarClientOnly: ComputedRef<boolean>
 
   hasAside: ComputedRef<boolean>
   leftAside: ComputedRef<boolean>