## MedplumClient.subscribeToCriteria() method [​](/content/docs/sdk/core.medplumclient.subscribetocriteria#medplumclientsubscribetocriteria-method "Direct link to MedplumClient.subscribeToCriteria(/index.html) method")

Subscribes to a given criteria, listening to notifications over WebSockets.

This uses Medplum's `WebSocket Subscriptions` under the hood.

A `SubscriptionEmitter` is returned from this function, which can be used to listen for updates to resources described by the given criteria.

When subscribing to the same criteria multiple times, the same `SubscriptionEmitter` will be returned, and a reference count will be incremented.

---

**Signature:**

```typescript
subscribeToCriteria(criteria: string, subscriptionProps?: Partial<Subscription>): SubscriptionEmitter;
```

## Parameters [​](/content/docs/sdk/core.medplumclient.subscribetocriteria#parameters "Direct link to Parameters"/index.html)

| Parameter        | Type                               | Description                                         |
| ---------------- | ---------------------------------- | --------------------------------------------------- |
| criteria         | string                             | The criteria to subscribe to.                       |
| subscriptionProps| Partial<Subscription>              | _(Optional)_ Optional properties to add to the created `Subscription` resource. |

**Returns:**

[SubscriptionEmitter](/content/docs/sdk/core.subscriptionemitter)

a `SubscriptionEmitter` that emits `Bundle` resources containing changes to resources based on the given criteria.

## Example [​](/content/docs/sdk/core.medplumclient.subscribetocriteria#example "Direct link to Example"/index.html)

```ts
const emitter = medplum.subscribeToCriteria('Communication');

emitter.addEventListener('message', (bundle: Bundle) => {

// Called when a `Communication` resource is created or modified

console.log(bundle?.entry?.[1]?.resource); // Logs the `Communication` resource that was updated
});
```

- [MedplumClient.subscribeToCriteria() method](/content/docs/sdk/core.medplumclient.subscribetocriteria#medplumclientsubscribetocriteria-method/index.html)  
- [Parameters](/content/docs/sdk/core.medplumclient.subscribetocriteria#parameters/index.html)  
- [Example](/content/docs/sdk/core.medplumclient.subscribetocriteria#example/index.html)