---
title: "Breaking: #78521 - Drop unused JavaScript from backend.js"
manual: "TYPO3 Core Changelog"
version: "main"
permalink: "https://docs.typo3.org/permalink/changelog:breaking-78521"
source: "Changelog/8.5/Breaking-78521-DropUnusedJavaScriptFromBackendjs.rst"
modified: "2026-09-14T09:47:36+00:00"
---

# Breaking: #78521 - Drop unused JavaScript from backend.js

See [forge#78521](https://forge.typo3.org/issues/78521)

## Description

The following JavaScript methods related to ExtJS have been removed from the Backend main frame
as defined in the main `backend.js` file.

-   `TYPO3._instances`
-   `TYPO3.addInstance`
-   `TYPO3.getInstance`
-   `TYPO3.helpers.split`

## Impact

Any call to one of the above mentioned methods will result in a JavaScript error.

## Affected Installations

Any installation that uses one of the methods mentioned above.