Update type and changeset

Signed-off-by: Dominik Henneke <dominik.henneke@sda-se.com>

.changeset/good-humans-draw.md

@@ -2,5 +2,5 @@
 '@backstage/plugin-app-backend': patch
 ---
 
-Add a `Cache-Control: no-store` header to the `index.html` response to instruct the browser to not cache the pages.
-This is a workaround for a missing `staticFallbackHandler` since an old `index.html` might link to static assets from a previous deployment.
+Add a `Cache-Control: no-store, max-age=0` header to the `index.html` response to instruct the browser to not cache the pages.
+This tells the browser to not serve a cached `index.html` that might link to static assets from a previous deployment that are not available anymore.

plugins/app-backend/src/service/router.ts

@@ -23,6 +23,9 @@ import { resolve as resolvePath } from 'path';
 import { Logger } from 'winston';
 import { injectConfig, readConfigs } from '../lib/config';
 
+// express uses mime v1 while we only have types for mime v2
+type Mime = { lookup(arg0: string): string };
+
 export interface RouterOptions {
   config: Config;
   logger: Logger;
@@ -101,8 +104,10 @@ export async function createRouter(
         // The Cache-Control header instructs the browser to not cache html files since it might
         // link to static assets from recently deployed versions. This is a workaround when no
         // staticFallbackHandler is configured.
-        // use `as any` since express uses mime v1 while we only have types for mime v2
-        if ((express.static.mime as any).lookup(path) === 'text/html') {
+        if (
+          ((express.static.mime as unknown) as Mime).lookup(path) ===
+          'text/html'
+        ) {
           res.setHeader('Cache-Control', 'no-store, max-age=0');
         }
       },