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[Home](./index.md) &gt; [@firebase/firestore](./firestore.md) &gt; [/](./firestore_.md) &gt; [runTransaction](./firestore_.runtransaction.md)

## runTransaction() function

Executes the given `updateFunction` and then attempts to commit the changes applied within the transaction. If any document read within the transaction has changed, Cloud Firestore retries the `updateFunction`<!-- -->. If it fails to commit after 5 attempts, the transaction fails.

The maximum number of writes allowed in a single transaction is 500.

<b>Signature:</b>

```typescript
export declare function runTransaction<T>(firestore: FirebaseFirestore, updateFunction: (transaction: Transaction) => Promise<T>): Promise<T>;
```

## Parameters

|  Parameter | Type | Description |
|  --- | --- | --- |
|  firestore | [FirebaseFirestore](./firestore_.firebasefirestore.md) | A reference to the Firestore database to run this transaction against. |
|  updateFunction | (transaction: [Transaction](./firestore_.transaction.md)<!-- -->) =&gt; Promise&lt;T&gt; | The function to execute within the transaction context. |

<b>Returns:</b>

Promise&lt;T&gt;

If the transaction completed successfully or was explicitly aborted (the `updateFunction` returned a failed promise), the promise returned by the `updateFunction `<!-- -->is returned here. Otherwise, if the transaction failed, a rejected promise with the corresponding failure error is returned.