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How do you queue and synchronize writes while offline and push them once online?

Rana Sunny 398 07 Jul 2025
IndexedDB indexeddb
Updated 07 Jul 2025
Rana Sunny
Rana Sunny

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Sunny Rana (born 25 December 1987) is an Indian cricketer. He made his List A debut for Uttarakhand in the 2018–19 Vijay Hazare Trophy on 20 September 2018. He made his first-class debut for Uttarakhand in the 2018–19 Ranji Trophy on 1 November 2018. He made his Twenty20 debut for Uttarakhand in the 2018–19 Syed Mushtaq Ali Trophy on 21 February 2019.

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1 Answers

Rana Sunny
Rana Sunny 07 Jul 2025
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To queue and synchronize writes while offline and push them once online (commonly used in offline-first web/mobile apps), you typically follow this pattern:

General Strategy

  • Queue Writes Locally (Offline)
    • Store write actions (create/update/delete) in an offline queue, such as:
      • IndexedDB (Web)
      • localStorage (not recommended for complex writes)
      • SQLite (Mobile)
      • Dexie.js or localForage (for easier IndexedDB handling)
  • Detect Online Status
    • Use window.navigator.onLine and listen for:
window.addEventListener("online", syncQueuedWrites);
  • Synchronize (Push) Writes When Online
    • On online event or app load (if online), process queued writes:
      • Read each queued item.
      • Send the write to the server.
      • If successful, remove the item from the queue.
      • Optionally handle retry logic and conflict resolution.

Sample (Dexie.js Example)

1. Define Your IndexedDB Store (Queue)

const db = new Dexie("OfflineWriteDB");
db.version(1).stores({
    items: '++id, type, payload',
});

2. Queue Write Action Offline

async function queueWrite(type, payload) {
    await db.items.add({ type, payload });
}

3. Sync When Online

async function syncQueuedWrites() {
    const allItems = await db.items.toArray();

    for (const item of allItems) {
        try {
            const response = await fetch('/api/sync', {
                method: 'POST',
                headers: { 'Content-Type': 'application/json' },
                body: JSON.stringify(item)
            });

            if (response.ok) {
                await db.items.delete(item.id); // remove if sync successful
            }
        } catch (err) {
            console.error("Sync failed for item", item.id, err);
            // Optionally retry or mark failed
        }
    }
}

4. Detect Online and Start Sync

window.addEventListener("online", syncQueuedWrites);

Considerations

Feature Notes
Conflict Resolution Server should return proper status/errors if conflicts occur (e.g. versioning, timestamps)
Deduplication Ensure you don't double-send operations (e.g., mark with IDs)
Background Sync (PWAs) Use Background Sync API for advanced use
Retries Exponential backoff or retry count in queue schema
Encryption Encrypt local storage if handling sensitive data

Tools/Libraries

  • Dexie.js – Simplified IndexedDB
  • localForage – Abstracts IndexedDB, WebSQL, localStorage
  • Workbox – Service Worker tooling for caching + background sync
  • RxDB, PouchDB – Full sync-capable offline-first databases
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