# Custom Data

Custom data is additional information that can be added to the default data of Stream Call.
It is an object with key-value pairs that can be attached to users, events, and pretty much almost every domain model in the Stream Video SDK.

The type definition is the following:

```typescript
export type Custom = {
  [key: string]: any; // where `any` should be JSON-serializable value
};
```

## Adding custom data

Adding extra data can be done through the Server-Side SDKs or through the Client SDKs.
In the Stream Video SDK, you can add extra data when creating/updating a user, event, reaction and other models.

As a simple example, let's see how you can add a new `topic` field to a `call` instance.

```typescript
const call = client.call(type, id);
await call.getOrCreate({
  data: { custom: { topic: "Monthly sync" } },
});

// or update a custom field
await call.update({
  custom: { topic: "Weekly sync" },
});
```

## Reading custom data

The custom data is exposed through the `custom` state property (and `custom$` observable):

```typescript
const call = client.call(type, id);
await call.getOrCreate();

const topic = call.state.custom?.topic;
console.log("The topic of the current call is:", topic);

call.state.custom$.subscribe((custom) => {
  console.log("The topic is changed to:", custom?.topic);
});
```


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This page was last updated at 2026-08-14T17:47:09.497Z.

For the most recent version of this documentation, visit [https://getstream.io/video/docs/javascript/advanced/custom-data/](https://getstream.io/video/docs/javascript/advanced/custom-data/).