Diagnosing Capacitor Storage Persistence Failures in Ionic Apps

Recognizable Condition

Data written through Capacitor Storage does not survive app restarts or device reboots, showing a persistence failure.

Diagnostic Overview

Ordered Checks

1. npm list @capacitor/filesystem – run in project root. Verify plugin is installed and version matches Capacitor core. If missing, install with npm install @capacitor/filesystem. Risk: outdated plugin may lack persistence support.
2. Check available storage space per platform (e.g., iOS 100 MB, Android 50 MB). Use platform docs; if quota is near limit, reduce data size or switch to a larger area. Risk: exceeding quota causes silent write failure.
3. Open console/logcat and look for errors such as “Capacitor: Unable to write to storage”. Note any write‑error messages. Expected: no errors during write. Risk: ignoring logs may hide permission issues.
4. Re‑run the write with await and verify immediate success. Example:
   

   await capacitor.filesystem.setItem('', '');

   Then read back:
   

   const result = await capacitor.filesystem.getItem(''); console.log(result);

   If the value is returned without error, the async step was correct. Risk: omitting await can cause race conditions and data loss.

Fixes Tied to Findings

• Plugin missing/outdated (a): Install or upgrade: npx cap sync. Ensure Capacitor version matches plugin version. Risk: version mismatch may break API.
• Quota exceeded (b): Increase quota via platform config (e.g., iOS `UIRequiresPersistentStorage` in Info.plist) or migrate to a different storage area like SQLite. Verify quota after change. Risk: misconfiguration can cause silent failure.
• Async write not awaited (c): Wrap all write calls in try { await ... } catch (e) { console.error(e); }. Ensure every setItem is awaited before subsequent logic. Risk: missing await leads to intermittent data loss.
• Platform sandbox restrictions (d): Add required config for iOS: edit Info.plist and insert UIRequiresPersistentStorage. For Android, ensure android:requestLegacyExternalStorage is set if targeting API 30+. Risk: missing config results in silent write failure on device.

Escalation Criteria

If after performing all ordered checks the data still does not persist, consider the following escalation steps:

• Confirm the device’s storage is not full; free space and retry.
• Test on a different device or emulator to rule out device‑specific sandbox limits.
• Upgrade Capacitor core and the filesystem plugin to the latest stable release, then repeat the diagnostic.
• Open a Capacitor issue with detailed logs, device OS version, and app code snippet for community or maintainer assistance.