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Home Interviews What are transactions in IndexedDB and why are they important? – MindStick
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ICSM Computer
ICSM Computer 02 Jul 2025
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In IndexedDB, a transaction is a wrapper around one or more operations that ensures data integrity and consistency. All read and write operations must happen inside a transaction.

Why Are Transactions Important?

  • Atomicity: All operations in a transaction succeed or fail together.
  • Isolation: Prevents conflicts from simultaneous operations.
  • Lifetime-controlled: Transactions auto-close after completing or timing out.
  • Required: You must use a transaction to read/write from object stores.

Syntax and Usage

const tx = db.transaction(['store1', 'store2'], 'readwrite');
const store = tx.objectStore('store1');
store.put({ id: 1, name: 'Alice' });

Parameters:

  • Store(s): A string or array of object store names.
  • Mode: "readonly" or "readwrite"

Transaction Example

const tx = db.transaction('users', 'readwrite');
const store = tx.objectStore('users');

store.add({ id: 1, name: 'Alice' });
store.put({ id: 1, name: 'Alice Updated' });
store.delete(2); // Optional: delete by id

tx.oncomplete = () => {
    console.log('Transaction complete.');
};

tx.onerror = () => {
    console.error('Transaction failed:', tx.error);
};

Transaction Modes

Mode Description
readonly Can only read data
readwrite Can read and write

Key Transaction Rules

  • Transactions auto-commit once all operations finish.
  • You cannot reuse a transaction once it's completed or errored.
  • Do not do async calls (like fetch) inside a transaction and expect the transaction to stay open — it will close immediately.

Tip: Multiple Stores in One Transaction

const tx = db.transaction(['users', 'orders'], 'readwrite');
const users = tx.objectStore('users');
const orders = tx.objectStore('orders');

users.put({ id: 1, name: "Alice" });
orders.add({ orderId: 101, userId: 1 });

This ensures both operations succeed or fail together.

Summary

  • Transactions are mandatory for all DB operations.
  • Ensure atomic, consistent changes.
  • Must be used with the correct mode and store name(s).
  • Automatically manage their lifecycle.
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