AJAX command to update a form's build ID causes an syntax error on old Internet Explorer version due to reserved constant

I came across a weird javascript bug in Internet Explorer 8 using plup and plupload on a Drupal 7.27 project. File upload/browse would not work with the following JavaScript error: "Expected identifier" on misc/ajax.js line 625. I was really stunned that Drupal Core uses this kind of syntax since expressions like "class" or "new" are reserved ones and can cause errors on IE if used like core currently does.

Bug appeared on Win7 IE8 + IE7, works after appling patch.

I changed the code so that it works now. Patch following soon.