<!-- Public documentation export; not library implementation source. -->
# INumberFormatter

[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.

## Extends

[IFormatter](https://docs.lumencharts.com/charting-library/api/IFormatter)

## formatChange {#formatchange}

```ts
formatChange?(currentPrice: number, prevPrice: number): string;
```

Use the type signature above and the integration guide for the owning capability.

| Parameter | Type | Required |
| --- | --- | --- |
| `currentPrice` | `number` | Yes |
| `prevPrice` | `number` | Yes |

## Related types

- [IFormatter](https://docs.lumencharts.com/charting-library/api/IFormatter)

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Documentation page: https://docs.lumencharts.com/charting-library/api/INumberFormatter