(dev-server) retry loading backend script in web-worker (#806)

Co-authored-by: Jed Fox <git@jedfox.com>

packages/desktop-client/src/browser-server.js

 /* globals importScripts, backend */
 let hasInitialized = false;
 
-self.addEventListener('message', e => {
+/**
+ * Sometimes the frontend build is way faster than backend.
+ * This results in the frontend starting up before backend is
+ * finished and thus the backend script is not available.
+ *
+ * The goal of this function is to retry X amount of times
+ * to retrieve the backend script with a small delay.
+ */
+const importScriptsWithRetry = async (script, { maxRetries = 5 } = {}) => {
+  try {
+    importScripts(script);
+  } catch (e) {
+    // Break if maxRetries has exceeded
+    if (maxRetries <= 0) {
+      throw e;
+    } else {
+      console.groupCollapsed(
+        `Failed to load backend, will retry ${maxRetries} more time(s)`,
+      );
+      console.log(e);
+      console.groupEnd();
+    }
+
+    // Attempt to retry after a small delay
+    await new Promise(resolve =>
+      setTimeout(async () => {
+        await importScriptsWithRetry(script, {
+          maxRetries: maxRetries - 1,
+        });
+        resolve();
+      }, 5000),
+    );
+  }
+};
+
+self.addEventListener('message', async e => {
   if (!hasInitialized) {
     let msg = e.data;
 
@@ -19,7 +54,10 @@ self.addEventListener('message', e => {
         return;
       }
 
-      importScripts(`${msg.publicUrl}/kcab/kcab.worker.${hash}.js`);
+      await importScriptsWithRetry(
+        `${msg.publicUrl}/kcab/kcab.worker.${hash}.js`,
+        { maxRetries: isDev ? 5 : 0 },
+      );
 
       backend.initApp(version, isDev, self).catch(err => {
         console.log(err);

upcoming-release-notes/806.md

+---
+category: Maintenance
+authors: [MatissJanis]
+---
+
+Retry loading backend script in web-workers (for local dev server)