diff --git a/frontend/package.json b/frontend/package.json
index cdce3ff..08a4445 100644
--- a/frontend/package.json
+++ b/frontend/package.json
@@ -17,6 +17,7 @@
     "filesize": "^9.0.11",
     "jwt-decode": "^3.1.2",
     "naive-ui": "^2.32.1",
+    "semaphore": "^1.1.0",
     "stream-browserify": "^3.0.0",
     "util": "^0.12.4",
     "vue": "^3.2.37",
@@ -25,6 +26,7 @@
   "devDependencies": {
     "@rushstack/eslint-patch": "^1.1.4",
     "@types/node": "^18.7.14",
+    "@types/semaphore": "^1.1.1",
     "@vitejs/plugin-vue": "^3.0.1",
     "@vitejs/plugin-vue-jsx": "^2.0.0",
     "@vue/eslint-config-prettier": "^7.0.0",
diff --git a/frontend/src/api/base.ts b/frontend/src/api/base.ts
index d90f2df..06b32b9 100644
--- a/frontend/src/api/base.ts
+++ b/frontend/src/api/base.ts
@@ -40,8 +40,14 @@ export const post_token_form = (
 			},
 			onUploadProgress: onProgress
 		})
-		.then((res) => res.data)
-		.catch((err) => err.response.data);
+		.then((res) => {
+			console.log(res);
+			return res.data;
+		})
+		.catch((err) => {
+			console.log(err);
+			return err.response.data;
+		});
 
 // eslint-disable-next-line @typescript-eslint/no-unused-vars
 export const get = (url: string) =>
diff --git a/frontend/src/api/util.ts b/frontend/src/api/util.ts
index 7e15900..f798baa 100644
--- a/frontend/src/api/util.ts
+++ b/frontend/src/api/util.ts
@@ -4,6 +4,16 @@ import jwtDecode from 'jwt-decode';
 import { isErrorResponse } from './base';
 import { refresh_token } from './auth';
 
+export async function update_token(
+	token: TokenInjectType
+): Promise<string | void> {
+	if (!token.jwt.value) return token.logout();
+	const new_token = await refresh_token(token.jwt.value);
+	if (isErrorResponse(new_token)) return token.logout();
+	token.setToken(new_token.jwt);
+	return new_token.jwt;
+}
+
 export async function check_token(
 	token: TokenInjectType
 ): Promise<string | void> {
@@ -13,10 +23,7 @@ export async function check_token(
 	// Expires in more than 60 Minute
 	if (payload.exp && payload.exp > Math.floor(Date.now() / 1000 + 60 * 60))
 		return token.jwt.value;
-	const new_token = await refresh_token(token.jwt.value);
-	if (isErrorResponse(new_token)) return token.logout();
-	token.setToken(new_token.jwt);
-	return new_token.jwt;
+	return update_token(token);
 }
 
 export type TokenInjectType = {
diff --git a/frontend/src/components/DirViewer/DirViewerTable.vue b/frontend/src/components/DirViewer/DirViewerTable.vue
index afdb759..de1edc4 100644
--- a/frontend/src/components/DirViewer/DirViewerTable.vue
+++ b/frontend/src/components/DirViewer/DirViewerTable.vue
@@ -33,6 +33,7 @@ import {
 	Delete,
 	Download
 } from '@vicons/carbon';
+import semaphore from 'semaphore';
 import NLink from '@/components/NLink.vue';
 import PreviewImage from '@/components/DirViewer/PreviewImage.vue';
 import createZipDialog from '@/components/DirViewer/CreateZipDialog';
@@ -59,6 +60,7 @@ const props = defineProps<{
 	showPreview: boolean;
 }>();
 
+const previewDownloadSem = semaphore(40);
 const checkedRows = ref<number[]>([]);
 const deleteNodes = ref<number[]>([]);
 const deleteDialog = ref();
@@ -222,7 +224,12 @@ const previewColumns: DataTableColumn<Responses.GetNodeEntry>[] = [
 			return node.isFile ? (
 				<Suspense>
 					{{
-						default: () => <PreviewImage node={node} />,
+						default: () => (
+							<PreviewImage
+								node={node}
+								sem={previewDownloadSem}
+							/>
+						),
 						fallback: () => <NSpin size="small" />
 					}}
 				</Suspense>
diff --git a/frontend/src/components/DirViewer/PreviewImage.vue b/frontend/src/components/DirViewer/PreviewImage.vue
index a33e0a5..bf77dfa 100644
--- a/frontend/src/components/DirViewer/PreviewImage.vue
+++ b/frontend/src/components/DirViewer/PreviewImage.vue
@@ -1,5 +1,6 @@
 <script setup async lang="ts">
 import type { TokenInjectType, Responses } from '@/api';
+import type { Semaphore } from 'semaphore';
 import { inject, ref } from 'vue';
 import { NImage, NIcon } from 'naive-ui';
 import { Image, Music, Video, Document } from '@vicons/carbon';
@@ -7,6 +8,7 @@ import { check_token, FS, isErrorResponse } from '@/api';
 
 const props = defineProps<{
 	node: Responses.GetNodeEntry;
+	sem: Semaphore;
 }>();
 
 enum fileTypes {
@@ -23,28 +25,35 @@ const success = ref(false);
 const data = ref('');
 const fileType = ref<fileTypes>(fileTypes.UNKNOWN);
 
-const token = await check_token(jwt);
-if (token) {
-	if (props.node.preview) {
-		const resp = await FS.download_preview(token, props.node.id);
-		if (!isErrorResponse(resp)) {
-			data.value = resp.data;
-			success.value = true;
+await new Promise<void>((resolve) => {
+	props.sem.take(async () => {
+		const token = await check_token(jwt);
+		if (token) {
+			if (props.node.preview) {
+				const resp = await FS.download_preview(token, props.node.id);
+				if (!isErrorResponse(resp)) {
+					data.value = resp.data;
+					success.value = true;
+				}
+			} else {
+				fileType.value = fileTypes.UNKNOWN;
+				const resp = await FS.get_type(token, props.node.id);
+				if (!isErrorResponse(resp)) {
+					if (resp.type.startsWith('image'))
+						fileType.value = fileTypes.IMAGE;
+					else if (resp.type.startsWith('application/pdf'))
+						fileType.value = fileTypes.PDF;
+					else if (resp.type.startsWith('audio'))
+						fileType.value = fileTypes.AUDIO;
+					else if (resp.type.startsWith('video'))
+						fileType.value = fileTypes.VIDEO;
+				}
+			}
 		}
-	} else {
-		fileType.value = fileTypes.UNKNOWN;
-		const resp = await FS.get_type(token, props.node.id);
-		if (!isErrorResponse(resp)) {
-			if (resp.type.startsWith('image')) fileType.value = fileTypes.IMAGE;
-			else if (resp.type.startsWith('application/pdf'))
-				fileType.value = fileTypes.PDF;
-			else if (resp.type.startsWith('audio'))
-				fileType.value = fileTypes.AUDIO;
-			else if (resp.type.startsWith('video'))
-				fileType.value = fileTypes.VIDEO;
-		}
-	}
-}
+		props.sem.leave();
+		resolve();
+	});
+});
 </script>
 
 <template>
diff --git a/frontend/src/components/UploadDialog/UploadFileDialog.vue b/frontend/src/components/UploadDialog/UploadFileDialog.vue
index 2e919fe..8338930 100644
--- a/frontend/src/components/UploadDialog/UploadFileDialog.vue
+++ b/frontend/src/components/UploadDialog/UploadFileDialog.vue
@@ -1,7 +1,7 @@
 <script setup lang="ts">
 import type { TokenInjectType, UploadFile } from '@/api';
 import { ref, inject } from 'vue';
-import { check_token } from '@/api';
+import { update_token } from '@/api';
 import UploadEntry from '@/components/UploadDialog/UploadEntry.vue';
 import { NCard } from 'naive-ui';
 
@@ -10,7 +10,7 @@ const jwt = inject<TokenInjectType>('jwt') as TokenInjectType;
 const entries = ref<typeof UploadEntry[]>([]);
 
 async function startUpload() {
-	const token = await check_token(jwt);
+	const token = await update_token(jwt);
 	if (!token) return;
 	const ents: typeof UploadEntry[] = entries.value;
 	const allProms: Promise<void>[] = [];
diff --git a/frontend/src/views/FSView.vue b/frontend/src/views/FSView.vue
index baa40ba..ea345e6 100644
--- a/frontend/src/views/FSView.vue
+++ b/frontend/src/views/FSView.vue
@@ -2,13 +2,15 @@
 import type { TokenInjectType, Responses } from '@/api';
 import { onBeforeRouteUpdate, useRoute, useRouter } from 'vue-router';
 import { inject, onBeforeMount, ref } from 'vue';
-import { NCard } from 'naive-ui';
+import { NCard, useMessage } from 'naive-ui';
 import { check_token, FS, isErrorResponse } from '@/api';
 import UploadField from '@/components/UploadDialog/UploadField.vue';
 import DirViewer from '@/components/DirViewer/DirViewer.vue';
 import FileViewer from '@/components/FileViewer/FileViewer.vue';
 import NLink from '@/components/NLink.vue';
+import { loadingMsgWrapper } from '@/utils';
 
+const message = useMessage();
 const router = useRouter();
 const route = useRoute();
 const jwt = inject<TokenInjectType>('jwt') as TokenInjectType;
@@ -22,7 +24,7 @@ function nameCompare(a: Responses.GetNodeEntry, b: Responses.GetNodeEntry) {
 	return aStr.localeCompare(bStr);
 }
 
-async function fetch_node(node_id: number) {
+const fetch_node = loadingMsgWrapper(message, async (node_id: number) => {
 	const token = await check_token(jwt);
 	if (!token) return;
 	const [p, n] = [
@@ -41,7 +43,7 @@ async function fetch_node(node_id: number) {
 		n.children = [...folders, ...files];
 	}
 	[path.value, node.value] = [p, n];
-}
+});
 
 onBeforeRouteUpdate(async (to) => {
 	await fetch_node(Number(to.params.node_id));
diff --git a/frontend/vite.config.ts b/frontend/vite.config.ts
index 3aadb42..5515038 100644
--- a/frontend/vite.config.ts
+++ b/frontend/vite.config.ts
@@ -13,6 +13,7 @@ export default defineConfig({
 		}
 	},
 	build: {
+		sourcemap: 'inline',
 		chunkSizeWarningLimit: 1024 * 1024
 	}
 });
diff --git a/frontend/yarn.lock b/frontend/yarn.lock
index d7c89df..c8cf203 100644
--- a/frontend/yarn.lock
+++ b/frontend/yarn.lock
@@ -421,6 +421,11 @@
   resolved "https://registry.yarnpkg.com/@types/node/-/node-17.0.45.tgz#2c0fafd78705e7a18b7906b5201a522719dc5190"
   integrity sha512-w+tIMs3rq2afQdsPJlODhoUEKzFP1ayaoyl1CcnwtIlsVe7K7bA1NGm4s3PraqTLlXnbIN84zuBlxBWo1u9BLw==
 
+"@types/semaphore@^1.1.1":
+  version "1.1.1"
+  resolved "https://registry.yarnpkg.com/@types/semaphore/-/semaphore-1.1.1.tgz#035baeec703fe8cf9f56a2b7af22bdda4f22d6ea"
+  integrity sha512-jmFpMslMtBGOXY2s7x6O8vBebcj6zhkwl0Pd/viZApo1uZaPk733P8doPvaiBbCG+R7201OLOl4QP7l1mFyuyw==
+
 "@typescript-eslint/eslint-plugin@^5.0.0":
   version "5.36.1"
   resolved "https://registry.yarnpkg.com/@typescript-eslint/eslint-plugin/-/eslint-plugin-5.36.1.tgz#471f64dc53600025e470dad2ca4a9f2864139019"
@@ -2317,6 +2322,11 @@ seemly@^0.3.6:
   resolved "https://registry.yarnpkg.com/seemly/-/seemly-0.3.6.tgz#7ef97e8083dea00804965e2662f572a5df9cb18e"
   integrity sha512-lEV5VB8BUKTo/AfktXJcy+JeXns26ylbMkIUco8CYREsQijuz4mrXres2Q+vMLdwkuLxJdIPQ8IlCIxLYm71Yw==
 
+semaphore@^1.1.0:
+  version "1.1.0"
+  resolved "https://registry.yarnpkg.com/semaphore/-/semaphore-1.1.0.tgz#aaad8b86b20fe8e9b32b16dc2ee682a8cd26a8aa"
+  integrity sha512-O4OZEaNtkMd/K0i6js9SL+gqy0ZCBMgUvlSqHKi4IBdjhe7wB8pwztUk1BbZ1fmrvpwFrPbHzqd2w5pTcJH6LA==
+
 "semver@2 || 3 || 4 || 5", semver@^5.5.0:
   version "5.7.1"
   resolved "https://registry.yarnpkg.com/semver/-/semver-5.7.1.tgz#a954f931aeba508d307bbf069eff0c01c96116f7"