Breaking: #98100 - Compression and Concatenation of JavaScript and CSS files for Backend removed

See forge#98100


TYPO3 Backend introduced Compression and Concatenation of CSS and JavaScript files in version 4.3 due to limitations of Internet Explorer 9 and lower. Since then, TYPO3 Backend uses JavaScript modules and loading via RequireJS and ES Modules, as well as CSS compression and concatenation by default during build time.

For this reason, this feature is removed from the actual ResourceCompressor, which only works in TYPO3 Frontend rendering now via the common TypoScript settings.


A custom handler for concatenation and compression of JS and CSS files has no effect anymore when registered in a third-party extension.

This could previously be configured via

  • $GLOBALS['TYPO3_CONF_VARS']['BE']['jsConcatenateHandler']

  • $GLOBALS['TYPO3_CONF_VARS']['BE']['jsCompressHandler']

  • $GLOBALS['TYPO3_CONF_VARS']['BE']['cssConcatenateHandler']

  • $GLOBALS['TYPO3_CONF_VARS']['BE']['cssCompressHandler']

Additionally, it was previously possible to configure a custom root path in ResourceCompressor via setRootPath($rootPath), which has been removed as well.

Affected installations

TYPO3 installations with custom JS and CSS handlers for TYPO3 Backend routines via custom extensions which is highly unlikely.


None, as component-based CSS files and module-based JS files are loaded already anyway, and the performance impact of loading multiple files is rather low due to optimized ".htaccess" configurations already, and through bundling all CSS for core in optimized files as well.