On 7 Aug 2015, at 13:05, S Page <spage@wikimedia.org> wrote:

On Thu, 06 Aug 2015 01:24:03 +0200, Krinkle <krinklemail@gmail.com> wrote:

TL:DR; Double-check your wiki's site scripts and your personal scripts
to ensure "document.write" is no longer used.

...
Check out the migration page for other deprecations and common issues you may encounter:
https://www.mediawiki.org/wiki/ResourceLoader/Migration_guide_(users)

I notice people have added document.write() migration advice to its "Good practices" section [1] (thanks! <3 ). There's other good advice there.