what is indexed let's look at the MDN definition of indexedDB: IndexedDB is a low-level API for client-side storage of significant amounts of structured data, including files/blobs.
so essentially we can use it when the local storage is too small for your needs.

note: IndexedDB is a mix between SQL and NoSQL databases as its a Transactional db like SQL databases but it also a js object oriented db like NOSQL databases

table

creating the database
creating the store
creating transaction
doing crud operation

IDBFactory{
    open(name, version?: number): // opening a database returns IDBOpenDBRequest
    deleteDatabase(name: string): 
    cmp(first: any, second: any): 
    databases(): 
}
IDBOpenDBRequest{
    onblocked:
    onupgradeneeded:
    addEventListener:
    removeEventListener:
    onerror:
    onsuccess:
    readonly readyState: 
    readonly result: 
    readonly source: 
    readonly transaction:
}
IDBDatabase{
    onabort: 
    onclose: 
    onerror:
    onversionchange:
    transaction:
    addEventListener:
    removeEventListener:
    deleteObjectStore:
    close:
    createObjectStore:
    readonly version:
}
IDBTransaction{
    readonly db: 
    readonly durability: 
    readonly error: 
    readonly mode: 
    readonly objectStoreNames: 
    onabort: 
    oncomplete: 
    onerror: 
    abort(): 
    commit(): 
    objectStore:
    addEventListener:
    removeEventListener:
}

simple diagram to show how to open the database and do simple crud operations as you can see all operations follow the same pattern doing action and then listening to the INDRequst for success or other response

1. Open a database and creating store

The open operation doesn't open the database right away or start a transaction right away it returns an object of type IDBOpenDBRequest in success and throws an error incase of an error.

most operation work the same way the return some type of IDBRequest for which u have to listen to success or error.

const request = window.indexedDB.open("databasename", 1);
request.onupgradeneeded = (event: IDBVersionChangeEvent) => {
    const db = request.result;
    if (!db.objectStoreNames.contains(storeName)) {
        // creating store if it doesnot exist
        db.createObjectStore(storeName);
    }
};
request.onsuccess = (e) => {
    console.log(e);  
};
request.onerror = (e) => {
    console.error(e);
}

2. getting access to the database and store

const db = request.result; // the request from the indexedDB.open()
const transaction = db.transaction(param.storename, 'readwrite');
const store = transaction.objectStore(param.storename);

3. doing crud operations

3.1 adding data

let request = store.add(data, key)
if (request) {
request.onsuccess = () => {
 // success
};
request.onerror = (e) => {
    throw new Error(e);
};

3.2 deleting data

const request = store.delete(param.data.key);
request.onsuccess = () => {
 // success
};
request.onerror = (e) => {
    throw new Error(e);
};

3.3 modifying data

const request = store.put(data, key);
request.onsuccess = () => {
 // success
};
request.onerror = (e) => {
    throw new Error(e);
};
);

3.4 getting specific collection data

indexedDb offer a way to have access to data at the same time the database is searching through the database store.openCursor

3.4.1 fetching all store data

let data = [];
store.openCursor().onsuccess = (event) => {
try {
const cursor = event.target.result;
if (cursor) {
data.push({ value: cursor.value, key: cursor.key });
cursor.continue();
} else {
console.log('finished');
}
} catch (e) {
 throw new Error(e);
}
};

you can convert all operation to asyncronous function for easy use
converting adding data to return a promise

const addData = async (db, storename, data, key) => {
    const transaction = db.transaction(param.storename, 'readwrite');
    const store = transaction.objectStore(param.storename);
    let request = store.add(data, key)
    if (request) {
    request.onsuccess = () => {
     // success
    };
    request.onerror = (e) => {
        throw new Error(e);
    };
}
await addData(db, "storename" , {/*somedata*/}, "key").

full code converted to async funciton at github

IndexedDb A bigger LocalStorage