# Property signature ActivityStartingState.additionalData

Data internal to the add-on that it can use to initialize itself. Useful for
communicating application-specific state to users joining the activity that
cannot be stored in the URLs. The length of this string must be less than 4,096
characters.

## Signature

    additionalData?: string;

## Details

| Type | `string` |
| Optional | Yes |
| Readonly | No |
|---|---|