[Home](./index.md) > [@firebase/firestore](./firestore.md) > [/](./firestore_.md) > [updateDoc](./firestore_.updatedoc.md) ## updateDoc() function Updates fields in the document referred to by the specified `DocumentReference`. The update will fail if applied to a document that does not exist. Signature: ```typescript export declare function updateDoc(reference: DocumentReference, data: UpdateData): Promise; ``` ## Parameters | Parameter | Type | Description | | --- | --- | --- | | reference | [DocumentReference](./firestore_.documentreference.md)<unknown> | A reference to the document to update. | | data | [UpdateData](./firestore_.updatedata.md) | An object containing the fields and values with which to update the document. Fields can contain dots to reference nested fields within the document. | Returns: Promise<void> A Promise resolved once the data has been successfully written to the backend (note that it won't resolve while you're offline).