## ReadablePromise.then() method

Attaches callbacks for the resolution and/or rejection of the Promise.

**Signature:**

```typescript
then<TResult1 = T, TResult2 = never>(onfulfilled?: ((value: T) => TResult1 | PromiseLike<TResult1>) | null, onrejected?: ((reason: any) => TResult2 | PromiseLike<TResult2>) | null): Promise<TResult1 | TResult2>;
```

## Parameters

| Parameter | Type | Description |
| --- | --- | --- |
| onfulfilled | ((value: T) => TResult1 \| PromiseLike<TResult1>) \| null | _(Optional)_ The callback to execute when the Promise is resolved. |
| onrejected | ((reason: any) => TResult2 \| PromiseLike<TResult2>) \| null | _(Optional)_ The callback to execute when the Promise is rejected. |

**Returns:**

Promise<TResult1 \| TResult2>

A Promise for the completion of which ever callback is executed.

- [ReadablePromise.then() method](/content/docs/sdk/core.readablepromise.then#readablepromisethen-method/index.html)
- [Parameters](/content/docs/sdk/core.readablepromise.then#parameters/index.html)