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Getting Started with Momento Vector Index in JavaScript

Momento provides two JavaScript SDKs; one for Node.js and one for browsers other web applications. The two SDKs have identical APIs, so your code will look the same except for import statements, but under the hood they are built for optimal performance and compatibility in different JavaScript runtime environments.

This page contains the basics that you will need in order to get going quickly with Momento Vector Index. For more in-depth information and examples, visit the SDK pages linked above.

Install the Momento SDK

To Install the Momento Node.js SDK in an existing Node.js project:

npm install @gomomento/sdk

OR, to install the Momento Web SDK in an existing browser application project:

npm install @gomomento/sdk-web

You only need one of the two libraries; either @gomomento/sdk or @gomomento/sdk-web, depending on your target platform. You do not need both.

Set up your API key

You'll need a Momento API key to authenticate with Momento. You can get one, preferably a fine-grained token, from the Momento Web Console. Once you have a token, store it in an environment variable so that the Momento client can consume it:

export MOMENTO_API_KEY=<your Momento token here>

Note: it is best practice to put the token into something like AWS Secret Manager or GCP Secret Manager instead of an environment variable for enhanced security, but we are using one here for demo purposes.

Import libraries and instantiate a vector index client

This code sets up the class with the necessary imports, the class definition, and the PreviewVectorIndexClient instantiation that each of the other functions will need to call.

import {CredentialProvider, PreviewVectorIndexClient, VectorIndexConfigurations} from "@gomomento/sdk";

const client = new PreviewVectorIndexClient({
configuration: VectorIndexConfigurations.Laptop.latest(),
credentialProvider: CredentialProvider.fromEnvironmentVariable({
environmentVariableName: 'MOMENTO_API_KEY',

The following examples assume that you have already instantiated a PreviewVectorIndexClient as shown above.

Create a new index in Momento Vector Index

Use this snippet to create a new index in your account. The similarityMetric parameter is optional and defaults to VectorSimilarityMetric.COSINE_SIMILARITY.

const indexName = "my-index";
// The number of dimensions in your vectors
const numDimensions = 2;
const similarityMetric = VectorSimilarityMetric.COSINE_SIMILARITY;

const createResponse = await client.createIndex(indexName, numDimensions, similarityMetric);
if (createResponse instanceof CreateVectorIndex.Success) {
console.log('Index created successfully!');
} else {
console.log(`Error creating index: ${createResponse.toString()}`);

Get list of existing indexes in your account

In this example, we list the indexes in your account.

const listResponse = await client.listIndexes();
if (listResponse instanceof ListVectorIndexes.Success) {
} else {
console.log(`Error listing indexes: ${listResponse.toString()}`);

Write a batch of items to the index

A simple example of doing an upsertItemBatch operation. This operation will insert the items if they don't exist, or replace them if they do.

const indexName = "my-index";
const upsertResponse = await client.upsertItemBatch(indexName, [
id: 'example_item_1',
vector: [1.0, 2.0],
metadata: {key1: 'value1'},
id: 'example_item_2',
vector: [3.0, 4.0],
metadata: {key2: 'value2'},
if (upsertResponse instanceof VectorUpsertItemBatch.Success) {
console.log('Successfully upserted items');
} else {
console.log(`Error adding items: ${upsertResponse.toString()}`);

Searching the index

This is an example of a search operation to get the top-k items from the index matching the queryVector. The metadataFields parameter is optional and can be used to specify which metadata fields to return in the response.

Here we use a queryVector of [1.0, 2.0] and ask for the top 2 results.

const indexName = "my-index";
const queryVector = [1.0, 2.0];
const searchResponse = await, queryVector, {
topK: 2,
metadataFields: ALL_VECTOR_METADATA,
if (searchResponse instanceof VectorSearch.Success) {
console.log(`Search succeeded with ${searchResponse.hits().length} results`);
} else {
console.log(`Error searching items: ${searchResponse.toString()}`);

Deleting items from the index

An example of deleting the items from an index using deleteItemBatch.

const indexName = "my-index";
const itemsToDelete = [

const deleteResponse = await client.deleteItemBatch(indexName, itemsToDelete);
if (deleteResponse instanceof VectorDeleteItemBatch.Success) {
console.log('Successfully deleted items');
} else {
console.log(`Error deleting items: ${deleteResponse.toString()}`);

Deleting an index

An example of deleting an index using deleteIndex.

const indexName = "my-index";
const deleteIndexResponse = await client.deleteIndex(indexName);
if (deleteIndexResponse instanceof DeleteVectorIndex.Success) {
console.log("Index 'test-index' deleted");
} else {
console.log(`Error deleting index: ${deleteIndexResponse.toString()}`);