feat: provide exported function

packages/nuxt/src/app/utils.ts

@@ -1,3 +1,64 @@
+import type {
+  AllowedComponentProps,
+  AnchorHTMLAttributes,
+  ComputedRef,
+  DefineComponent,
+  InjectionKey, PropType,
+  VNodeProps
+} from 'vue'
+import { computed, defineComponent, h, inject, onBeforeUnmount, onMounted, provide, ref, resolveComponent } from 'vue'
+import type { RouteLocation, RouteLocationRaw, Router, RouterLinkProps } from '#vue-router'
+import { hasProtocol, joinURL, parseQuery, parseURL, withTrailingSlash, withoutTrailingSlash } from 'ufo'
+import { preloadRouteComponents } from './composables/preload'
+import { onNuxtReady } from './composables/ready'
+import { navigateTo, useRouter } from './composables/router'
+import { useNuxtApp, useRuntimeConfig } from './nuxt'
+import { cancelIdleCallback, requestIdleCallback } from './idle-callback'
+
 export function toArray<T> (value: T | T[]): T[] {
   return Array.isArray(value) ? value : [value]
 }
+
+export type CallbackFn = () => void
+type ObserveFn = (element: Element, callback: CallbackFn) => () => void
+
+function useObserver (): { observe: ObserveFn } | undefined {
+  if (import.meta.server) { return }
+
+  const nuxtApp = useNuxtApp()
+  if (nuxtApp._observer) {
+    return nuxtApp._observer
+  }
+
+  let observer: IntersectionObserver | null = null
+
+  const callbacks = new Map<Element, CallbackFn>()
+
+  const observe: ObserveFn = (element, callback) => {
+    if (!observer) {
+      observer = new IntersectionObserver((entries) => {
+        for (const entry of entries) {
+          const callback = callbacks.get(entry.target)
+          const isVisible = entry.isIntersecting || entry.intersectionRatio > 0
+          if (isVisible && callback) { callback() }
+        }
+      })
+    }
+    callbacks.set(element, callback)
+    observer.observe(element)
+    return () => {
+      callbacks.delete(element)
+      observer!.unobserve(element)
+      if (callbacks.size === 0) {
+        observer!.disconnect()
+        observer = null
+      }
+    }
+  }
+
+  const _observer = nuxtApp._observer = {
+    observe
+  }
+
+  return _observer
+}