The list of JavaScript deprecations suggests that importScript is/will be deprecated in favor of mediaWiki.loader functionality. Nonetheless, it doesn't seems to support a nice syntax like importScript( 'Page.js' );
So, it would be interesting to provide support to such a syntax before deprecating the legacy importScript function.
Version: unspecified
Severity: enhancement
URL: http://www.mediawiki.org/w/index.php?title=ResourceLoader/JavaScript_Deprecations#wikibits.js