What are indexes in IndexedDB and how do you use them?

Question

Manish Sharma · Answer

In IndexedDB, an index is a special data structure that lets you
quickly search and retrieve records by a property other than the primary key (keyPath).
What is an Index?
An index maps values of a property to their corresponding records, allowing efficient
queries and lookups.Think of it like SQL CREATE INDEX on a column.Great for filtering, searching, or sorting on non-primary-key fields.
Example: When to Use Indexes
Suppose your object store is:
{ id: 1, name: "Alice", email: "alice@example.com" }
You can:
Use "id" as the primary key (keyPath)Create an index on "email" for quick lookup
How to Create an Index
Indexes are created in the onupgradeneeded event when the database schema is defined or upgraded.
const request = indexedDB.open("UserDB", 2);
request.onupgradeneeded = (event) =andgt; {
    const db = event.target.result;
    // Create object store if not already exists
    const userStore = db.objectStoreNames.contains("users")
        ? event.target.transaction.objectStore("users")
        : db.createObjectStore("users", { keyPath: "id" });
    // Create index on 'email' field
    userStore.createIndex("emailIndex", "email", { unique: true });
};
"emailIndex" = name of the index"email" = path to the field being indexed{ unique: true } = prevents duplicate values for that index
How to Use an Index (Query)
function getUserByEmail(db, email) {
    return new Promise((resolve, reject) =andgt; {
        const tx = db.transaction("users", "readonly");
        const store = tx.objectStore("users");
        const index = store.index("emailIndex");
        const request = index.get(email); // fast lookup by email
        request.onsuccess = () =andgt; resolve(request.result);
        request.onerror = () =andgt; reject(request.error);
    });
}
You can also use:
index.getAll(value)index.openCursor() for iterationindex.count() to count matches
Example: Get All Users by Country
// In onupgradeneeded
store.createIndex("countryIndex", "country");
// Later
const index = db.transaction("users").objectStore("users").index("countryIndex");
index.getAll("India").onsuccess = (e) =andgt; {
    console.log("All users from India:", e.target.result);
};
Benefits of Using Indexes
Feature
Benefit
Fast search
Lookup by fields other than primary key
Filtering
Get records that match specific criteria
Sorting
Use .openCursor() with direction
Uniqueness
Enforce unique values on fields
Summary
Indexes improve read performance by allowing efficient queries on object properties.Define them in onupgradeneeded using createIndex(name, keyPath, options).Query using store.index('indexName').get(...), getAll(), or
openCursor().

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What are indexes in IndexedDB and how do you use them?

Manish Sharma

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1 Answers

What is an Index?

Example: When to Use Indexes

How to Create an Index

How to Use an Index (Query)

Example: Get All Users by Country

Benefits of Using Indexes

Summary

Liked By

Feature	Benefit
Fast search	Lookup by fields other than primary key
Filtering	Get records that match specific criteria
Sorting	Use `.openCursor()` with direction
Uniqueness	Enforce unique values on fields