Created attachment 3704 [details] Fix I still need to write a layout test for this.
Comment on attachment 3704 [details] Fix The "containsNaN" function seems like it will go past even the 7th argument, which is probably not the desired behavior. You probably want a maxArgs parameter to that function. Also, that change doesn't seem to be part of the bug fix. So maybe you should land it separately. The main bug fix looks fine, r=me on that. I'm going to set this to review+, but it's really review+ on the first half ot he patch and review- on the second half.
Created attachment 3805 [details] fast/js/date-big-setmonth.html Layout test
OK. I landed the setMonth change minus the containsNaN bit plus the layout test.