Advanced level · Module 6: JavaScript Capstone Project · Lesson 4 of 5
Sync, Quality and Audits
Connect the front end to the API with retrying sync, then audit performance, security and accessibility.
In this lesson you will
- Implement reliable background sync with retries
- Audit and fix performance, security and accessibility issues
Key concepts
sync on reconnectretry with backoffaudit checklistevidence
The lesson
Sync pending visits when the app starts, when the online event fires and on demand. Retry failures with increasing delays and mark visits synced only after the server confirms them.
Test the hard cases: losing the connection mid-sync, syncing twice, server validation errors and a very large backlog.
Run the audits from the previous module — Lighthouse on mobile settings, an XSS review, a keyboard and screen-reader test — and fix the most important issues, recording evidence.
Step by step
- Implement sync with retries and status updates.
- Test dropped connections and double syncs.
- Run the three audits.
- Fix the top issues and record evidence.
Practice activity
Complete milestone 4: working sync and an audit report.
Expected result: Sync handles every tested failure without duplicates, and the audit report shows fixes with evidence.
Check your understanding
-
When should a visit be marked synced?
Show answer
Only after the server confirms it was stored.
-
Name two events that should trigger a sync attempt.
Show answer
App start and the browser's online event (or a manual sync).
Taught live by an instructor — online or in person. Free course lessons are for self-study and do not lead to a certificate — see registration options.