This example demonstrates a basic subscription operation in Apollo Server. See the docs on subscriptions

The example server exposes one subscription (numberIncremented) that returns an integer that's incremented on the server every second.

After you start up this server, you can test out running a subscription with the Apollo Studio Explorer by following the link from http://localhost:4000/graphql to the Apollo Sandbox. You might need to edit the Apollo Sandbox connection settings to select the graphql-ws subscriptions implementation. You'll see the subscription's value update every second.

subscription IncrementingNumber {
  numberIncremented
}

npm install
npm start