Massive JS Client

Welcome to the official JS client library for the Massive REST and WebSocket API. To get started, please see the Getting Started section in our documentation, view the examples directory for code snippets, or the blog post with video tutorials to learn more. To generate the package documentation please run npm run generate-doc.

For upgrade instructions please see the Release Notes.

Note: Polygon.io has rebranded as Massive.com on Oct 30, 2025. Existing API keys, accounts, and integrations continue to work exactly as before. The only change in this SDK is that it now defaults to the new API base at api.massive.com, while api.polygon.io remains supported for an extended period.

For details, see our rebrand announcement blog post or open an issue / contact [email protected] if you have questions.

Getting the client

To get started, you'll need to install the client library:

npm install --save '@massive.com/client-js'

Next, create a new client with your API key.

import { restClient } from '@massive.com/client-js';
const rest = restClient(process.env.POLY_API_KEY);

Using the client

After creating the client, making calls to the Massive API is easy. For example, here's a complete example on how to get aggregates (bars):

import { restClient } from '@massive.com/client-js';

const apiKey = "XXXX";
const rest = restClient(apiKey, 'https://api.massive.com');

async function example_getStocksAggregates() {
  try {
    const response = await rest.getStocksAggregates(
      {
        stocksTicker: "AAPL",
        multiplier: "1",
        timespan: "day",
        from: "2025-11-01",
        to: "2025-11-30",
        adjusted: "true",
        sort: "asc",
        limit: "120"
      }
    );
    console.log('Response:', response);
  } catch (e) {
    console.error('An error happened:', e);
  }
}

example_getStocksAggregates();

Or, maybe you want to get the last trades or quotes for a ticker:

import { restClient } from '@massive.com/client-js';

const apiKey = "XXXX";
const rest = restClient(apiKey, 'https://api.massive.com');

async function example_getLastStocksTrade() {
  try {
    const response = await rest.getLastStocksTrade("AAPL");
    console.log('Response:', response);
  } catch (e) {
    console.error('An error happened:', e);
  }
}

example_getLastStocksTrade();

import { restClient } from '@massive.com/client-js';

const apiKey = "XXXXX";
const rest = restClient(apiKey, 'https://api.massive.com');

async function example_getLastStocksQuote() {
  try {
    const response = await rest.getLastStocksQuote("AAPL");
    console.log('Response:', response);
  } catch (e) {
    console.error('An error happened:', e);
  }
}

example_getLastStocksQuote();

Finally, maybe you want a snapshot of a ticker:

import { restClient } from '@massive.com/client-js';

const apiKey = "XXXXX";
const rest = restClient(apiKey, 'https://api.massive.com');

async function example_getStocksSnapshotTicker() {
  try {
    const response = await rest.getStocksSnapshotTicker("AAPL");
    console.log('Response:', response);
  } catch (e) {
    console.error('An error happened:', e);
  }
}

example_getStocksSnapshotTicker();

See full examples for more details on how to use this client effectively.

Pagination

The client can handle pagination for you through the globalFetchOptions by turning on the pagination: true option. The feature will automatically fetch all next_url pages of data when the API response indicates more data is available.

import { restClient } from '@massive.com/client-js';

const globalFetchOptions = {
	pagination: true,
};
const rest = restClient(process.env.POLY_API_KEY, "https://api.massive.com", globalFetchOptions);

rest.getStocksAggregates({
  stocksTicker: "AAPL",
  multiplier: "1",
  timespan: "day",
  from: "2025-11-01",
  to: "2025-11-30"
}).then((response) => {
	const data = response.data; // convert axios-wrapped response
	const resultCount = data.resultsCount;
	console.log("Result count:", resultCount);
}).catch(e => {
	console.error('An error happened:', e);
});

If there is a next_url field in the API response, the client will recursively fetch the next page for you, and then pass along the accumulated data.

WebSocket Client

Import the Websocket client and models packages to get started. You can get preauthenticated websocket clients for the 3 topics.

import { websocketClient } from "@massive.com/client-js";
const stocksWS = websocketClient(process.env.POLY_API_KEY, 'wss://delayed.massive.com').stocks();

stocksWS.onmessage = ({response}) => {
  const [message] = JSON.parse(response);

  stocksWS.send('{"action":"subscribe", "params":"AM.MSFT,A.MSFT"}');

  switch (message.ev) {
    case "AM":
      // your trade message handler
      break;
    case "A":
      // your trade message handler
      break;
  }
};

stocksWS.send({ action: "subscribe", params: "T.MSFT" });

See full examples for more details on how to use this client effectively.

Contributing

If you found a bug or have an idea for a new feature, please first discuss it with us by submitting a new issue. We will respond to issues within at most 3 weeks. We're also open to volunteers if you want to submit a PR for any open issues but please discuss it with us beforehand. PRs that aren't linked to an existing issue or discussed with us ahead of time will generally be declined. If you have more general feedback or want to discuss using this client with other users, feel free to reach out on our Slack channel.