#78

frontend/src/components/PostList.tsx

@@ -1,16 +1,19 @@
 import { Link } from 'react-router-dom'
 
+import type { MouseEvent } from 'react'
 import type { Post } from '@/types'
 
-type Props = { posts: Post[] }
+type Props = { posts:     Post[]
+	       onClick?:  (event: MouseEvent<HTMLElement>) => void }
 
 
-export default ({ posts }: Props) => (
+export default ({ posts, onClick }: Props) => (
     <div className="flex flex-wrap gap-6 p-4">
       {posts.map ((post, i) => (
 	  <Link to={`/posts/${ post.id }`}
 		key={i}
-		className="w-40 h-40 overflow-hidden rounded-lg shadow-md hover:shadow-lg">
+		className="w-40 h-40 overflow-hidden rounded-lg shadow-md hover:shadow-lg"
+		onClick={onClick}>
 	    <img src={post.thumbnail || post.thumbnailBase || undefined}
 		 alt={post.title || post.url}
 		 title={post.title || post.url || undefined}

frontend/src/main.tsx

@@ -1,4 +1,3 @@
-import { StrictMode } from 'react'
 import { createRoot } from 'react-dom/client'
 import { HelmetProvider } from 'react-helmet-async'
 
@@ -8,8 +7,6 @@ import App from '@/App'
 const helmetContext = { }
 
 createRoot (document.getElementById ('root')!).render (
-    <StrictMode>
-      <HelmetProvider context={helmetContext}>
-	<App />
-      </HelmetProvider>
-    </StrictMode>)
+    <HelmetProvider context={helmetContext}>
+      <App />
+    </HelmetProvider>)

frontend/src/pages/posts/PostListPage.tsx

@@ -1,8 +1,8 @@
 import axios from 'axios'
 import toCamel from 'camelcase-keys'
-import { useEffect, useRef, useState } from 'react'
+import { useEffect, useLayoutEffect, useRef, useState } from 'react'
 import { Helmet } from 'react-helmet-async'
-import { Link, useLocation } from 'react-router-dom'
+import { Link, useLocation, useNavigationType } from 'react-router-dom'
 
 import PostList from '@/components/PostList'
 import TagSidebar from '@/components/TagSidebar'
@@ -15,23 +15,29 @@ import type { Post, WikiPage } from '@/types'
 
 
 export default () => {
+  const navigationType = useNavigationType ()
+
+  const containerRef = useRef<HTMLDivElement | null> (null)
+  const loaderRef = useRef<HTMLDivElement | null> (null)
+
   const [cursor, setCursor] = useState ('')
   const [loading, setLoading] = useState (false)
   const [posts, setPosts] = useState<Post[]> ([])
   const [wikiPage, setWikiPage] = useState<WikiPage | null> (null)
 
-  const loaderRef = useRef<HTMLDivElement | null> (null)
-
   const loadMore = async (withCursor: boolean) => {
     setLoading (true)
+
     const res = await axios.get (`${ API_BASE_URL }/posts`, {
 	params: { tags:   tags.join (' '),
 		  match:  anyFlg ? 'any' : 'all',
-		  ...(withCursor ? { cursor } : { }) } })
+		  limit:  '20',
+		  ...(withCursor && { cursor }) } })
     const data = toCamel (res.data as any, { deep: true }) as { posts:      Post[]
 								nextCursor: string }
     setPosts (posts => [...(withCursor ? posts : []), ...data.posts])
     setCursor (data.nextCursor)
+
     setLoading (false)
   }
 
@@ -55,9 +61,25 @@ export default () => {
     }
   }, [loaderRef, loading])
 
-  useEffect (() => {
-    setPosts ([])
-    loadMore (false)
+  useLayoutEffect (() => {
+    const savedState = sessionStorage.getItem ('posts')
+    if (savedState && navigationType === 'POP')
+      {
+	const { posts, cursor, scroll } = JSON.parse (savedState)
+	setPosts (posts)
+	setCursor (cursor)
+
+	if (containerRef.current)
+	  containerRef.current.scrollTop = scroll
+
+	loadMore (true)
+      }
+    else
+      {
+	setPosts ([])
+	loadMore (false)
+      }
+    sessionStorage.removeItem ('posts')
 
     setWikiPage (null)
     if (tags.length === 1)
@@ -78,7 +100,7 @@ export default () => {
   }, [location.search])
 
   return (
-      <div className="md:flex md:flex-1">
+      <div className="md:flex md:flex-1" ref={containerRef}>
 	<Helmet>
 	  <title>
 	    {tags.length
@@ -93,7 +115,13 @@ export default () => {
 	  <TabGroup>
 	    <Tab name="広場">
 	      {posts.length
-	       ? <PostList posts={posts} />
+	       ? (
+		  <PostList posts={posts} onClick={() => {
+		    const statesToSave = {
+			posts, cursor,
+			scroll: containerRef.current?.scrollTop ?? 0 }
+		    sessionStorage.setItem ('posts', JSON.stringify (statesToSave))
+		  }} />)
 	       : !(loading) && '広場には何もありませんよ．'}
 	      {loading && 'Loading...'}
 	      <div ref={loaderRef} className="h-12"></div>