What happens during the onupgradeneeded event?

Question

ICSM Computer · Answer

The **onupgradeneeded** event in IndexedDB is triggered when:
A database is created for the first time, orYou open the database with a higher version number than the existing one.
It’s the only place where you can safely define or update the database schema, such as:
Creating
object storesAdding or modifying
indexesMigrating or transforming existing data
When Does onupgradeneeded Run?
Scenario
Triggered?
First time opening the DB
Yes
Opening DB with higher version number
Yes
Opening DB with same version number
No
What Can You Do in onupgradeneeded?
Typical Tasks:
Create object stores:
db.createObjectStore('users', { keyPath: 'id' });
Create indexes:
store.createIndex('emailIndex', 'email', { unique: true });
Rename or migrate data (for upgrades)Delete or recreate outdated object stores
Example
const request = indexedDB.open('MyAppDB', 2); // version 2 triggers upgrade
request.onupgradeneeded = function(event) {
    const db = event.target.result;
    if (!db.objectStoreNames.contains('users')) {
        db.createObjectStore('users', { keyPath: 'id' });
    }
    const userStore = event.target.transaction.objectStore('users');
    if (!userStore.indexNames.contains('emailIndex')) {
        userStore.createIndex('emailIndex', 'email', { unique: true });
    }
    console.log('Upgrade complete.');
};
Important Notes
This event is mandatory for schema upgrades — it’s the only place you can alter the structure.You must not read/write outside of transactions in this event — use the
event.target.transaction.
Summary
Feature
Description
When it triggers
On first open or version upgrade
What it does
Schema creation or modification (stores, indexes)
Access object stores
Via event.target.result and event.target.transaction
Transaction type
Auto-created versionchange transaction (read/write)
and

interview

What happens during the onupgradeneeded event?

ICSM Computer

Can you answer this question?

1 Answers

When Does `onupgradeneeded` Run?

What Can You Do in `onupgradeneeded`?

Typical Tasks:

Example

Important Notes

Summary

Liked By

Scenario	Triggered?
First time opening the DB	Yes
Opening DB with higher version number	Yes
Opening DB with same version number	No

Feature	Description
When it triggers	On first open or version upgrade
What it does	Schema creation or modification (stores, indexes)
Access object stores	Via `event.target.result` and `event.target.transaction`
Transaction type	Auto-created versionchange transaction (read/write)