Why your javascript on Wikipedia will break

This week we did our first roll out of MediaWiki 1.19 on some of the smaller project sites. This staged roll out is a great way to find out how you are using the software in ways we didn’t expect and to give you a warning: “Beware! This thing you are doing is going to break!” Of course, I would prefer to avoid that wherever possible, but there are things I can’t control.

So now, I get to say “Beware!”:

Beware!

If are using document.write() in some javascript, whether in a gadget, in your common.js, vector.js, monobook.js or even global.js, you need to change it. In the cases that I saw, people had used a code fragment like the following:

function importAnyScript(lang,family,script) {
document.write('<script type="text/javascript" src="' + 'http://'
        + lang + '.'
        + family + '.org/w/index.php?title='
        + script + '&action=raw&ctype=text/javascript"></script>');

This has to be changed to something like the following:

function importAnyScript(lang,family,script) {
mw.loader.load('//' + lang + '.' + family
        + '.org/w/index.php?title='
        + script + '&action=raw&ctype=text/javascript');
}