# IObservable [Integration guide](https://docs.lumencharts.com/charting-library/reference/compatibility) · [Reference index](https://docs.lumencharts.com/charting-library/api/) Public contract reference. This declaration describes types and callback shapes; availability is constrained by the linked integration guide and the runtime capability. Legacy product-specific fields are not a promise of implementation. ## subscribe {#subscribe} ```ts subscribe(callback: (value: T) => void): void; ``` Use the type signature above and the integration guide for the owning capability. | Parameter | Type | Required | | --- | --- | --- | | `callback` | `(value: T) => void` | Yes | ## unsubscribe {#unsubscribe} ```ts unsubscribe(callback: (value: T) => void): void; ``` Use the type signature above and the integration guide for the owning capability. | Parameter | Type | Required | | --- | --- | --- | | `callback` | `(value: T) => void` | Yes | --- Documentation page: https://docs.lumencharts.com/charting-library/api/IObservable