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 support@massive.com 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.MASSIVE_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.MASSIVE_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.MASSIVE_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.

Developing the client

Most users only need the published npm package above. This section is for contributors who want to build the client from source or regenerate it from the OpenAPI spec.

How the code is organized

• Generated — src/rest/ is generated from the OpenAPI spec by openapi-generator (typescript-axios). Do not edit it by hand; it is overwritten on every regeneration.
• Hand-written — src/main.ts (the restClient / MassiveClient glue and auto-pagination) and the entire WebSocket client under src/websockets/. These are never touched by regeneration.
• Committed spec — src/openapi.json is the filtered spec the client is generated from, committed so spec changes are visible in diffs.

Prerequisites

• Node.js 18+ (CI uses 22)
• A JDK 17+ on your PATH — the typescript-axios generator is a Java tool. No local JDK? Use the Docker recipe below.

Clone, build, and verify

git clone git@github.com:massive-com/client-js.git
cd client-js
npm ci

# Pulls the latest spec, regenerates src/rest, and bundles to dist/
npm run build

If you don't have a JDK locally, build inside a container that has both Node and Java (the generator needs Java):

docker run --rm -it -v "$(pwd)":/app -w /app node:22-bookworm sh -c \
  "apt-get update && apt-get install -y openjdk-17-jre-headless && npm ci && npm run build"

Verify the build produced a working client with a runnable REST example. Save this as verify.mjs in the repo root and run MASSIVE_API_KEY=your_key node verify.mjs:

import { restClient } from './dist/main.js';

const rest = restClient(process.env.MASSIVE_API_KEY, 'https://api.massive.com');

const response = await rest.getStocksAggregates({
  stocksTicker: 'AAPL',
  multiplier: '1',
  timespan: 'day',
  from: '2023-01-09',
  to: '2023-02-10',
  adjusted: 'true',
  sort: 'asc',
  limit: '120',
});
console.log('Aggregates results:', response.results?.length);

And a runnable WebSocket example (MASSIVE_API_KEY=your_key node ws-verify.mjs):

import { websocketClient } from './dist/main.js';

const stocksWS = websocketClient(process.env.MASSIVE_API_KEY, 'wss://delayed.massive.com').stocks();

stocksWS.onopen = () => stocksWS.send('{"action":"subscribe","params":"AM.MSFT"}');
stocksWS.onmessage = ({ data }) => {
  const messages = JSON.parse(data);
  for (const message of messages) console.log('WS message:', message);
};
stocksWS.onerror = (e) => console.error('WS error:', e);

Regenerating from the spec

Regeneration is a single command that pulls the latest spec, runs the generator, and leaves src/rest/ deterministic (hand-written code untouched):

npm run generate      # runs scripts/generate.sh: pull spec -> generate -> gate

The generator version is pinned in openapitools.json (currently 7.21.0) so diffs reflect spec changes, not generator upgrades. Spec filtering and the operation-id → method-name mapping live in scripts/pull_spec.js and scripts/operation-mappings.js.

Automated daily sync

.github/workflows/sync-openapi.yml runs every day (and on manual dispatch). It:

1. Pulls the latest spec from https://api.massive.com/openapi and regenerates the client with scripts/generate.sh.
2. Opens a brand-new PR (bot/openapi-sync-<date>-<run-id> → master, [bot]-prefixed title) only when the regenerated output differs from what's committed — no diff, no PR. The commit is GPG-signed as the bot identity and a Slack notification is posted.

Required repo secrets: GPG_PRIVATE_KEY, SLACK_CLIENT_LIBRARY_WEBHOOK (GITHUB_TOKEN is provided automatically). Every run opens a new PR and never reuses an existing one, so the reviewer always differs from the author.

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.