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Home Interviews How do you iterate over records using a cursor in IndexedDB? – MindStick
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1 Answers

Rana Sunny
Rana Sunny 03 Jul 2025
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You can iterate over records in IndexedDB using a cursor, which allows you to go through each record one-by-one—great for large datasets or conditional processing.

Basic Syntax for Cursor Iteration

const request = indexedDB.open("MyDB", 1);

request.onsuccess = function (event) {
    const db = event.target.result;
    const transaction = db.transaction("users", "readonly");
    const store = transaction.objectStore("users");

    const cursorRequest = store.openCursor(); // You can pass key ranges too

    cursorRequest.onsuccess = function (event) {
        const cursor = event.target.result;
        if (cursor) {
            console.log("Key:", cursor.key, "Value:", cursor.value);

            // Move to next record
            cursor.continue();
        } else {
            console.log("No more entries.");
        }
    };

    cursorRequest.onerror = function (event) {
        console.error("Cursor error:", event.target.error);
    };
};

You Can Use Cursor With:

Type Example
Whole object store store.openCursor()
Index index.openCursor()
Range query store.openCursor(IDBKeyRange.bound(1, 100))
Direction store.openCursor(null, 'prev')

Example: Read All Users Where Age > 30

store.openCursor().onsuccess = function (event) {
    const cursor = event.target.result;
    if (cursor) {
        const user = cursor.value;
        if (user.age > 30) {
            console.log("User over 30:", user);
        }
        cursor.continue();
    }
};

Cursor Methods

Method Purpose
cursor.continue() Move to next record (default)
cursor.advance(n) Skip n records
cursor.update(value) Update current record
cursor.delete() Delete current record

Update Record During Iteration

if (cursor.value.active === false) {
    const updated = { ...cursor.value, active: true };
    cursor.update(updated);
}

Summary

Feature Supported in Cursor
Loop through all Yes
Filter conditionally Yes (custom JS logic)
Read/write/delete Yes (in readwrite mode)
Performance Efficient for large data
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