137342 2014-10-02 05:12:24 -0700 Incorrect adding time to Date object for January 1st 2014-10-02 23:58:48 -0700 1 1 1 Unclassified WebKit JavaScriptCore 528+ (Nightly build) PC Windows 8 NEW InRadar P2 Major --- 1 justvamp webkit-unassigned ggaren mark.lam oldest_to_newest 1038849 0 justvamp 2014-10-02 05:12:24 -0700 Reproducing: Run this script: <script> var dt = new Date(); dt.setYear(2008); // any of these years: 1991, 2002, 2008, 2013, 2019, 2030, 2036, 2041, 2047, 2058... dt.setMonth(0, 1); // January 1st dt.setHours(23); dt.setMinutes(30); dt.setSeconds(0); console.log(dt.toString()); dt.setMinutes(dt.getMinutes() + 30) console.log(dt.toString()); </script> Excepted result (it works this way for other dates/years): Thu Jan 01 2008 23:30:00 GMT+0300 Fri Jan 02 2008 00:00:00 GMT+0300 But we have: Tue Jan 01 2008 23:30:00 GMT+0300 Tue Jan 01 2008 23:00:00 GMT+0300 This bug seems to be reproduced only for January 1st and only for years like 1991, 2002, 2008, 2013, 2019, 2030, 2036, 2041, 2047, 2058... === Also please take a look at another testcase. It's also pretty weird: <script> var dt = new Date(); dt.setYear(2008); // any of these years: 1991, 2002, 2008, 2013, 2019, 2030, 2036, 2041, 2047, 2058... dt.setMonth(0, 1); // January 1st dt.setHours(23); dt.setMinutes(30); dt.setSeconds(0); console.log(dt.toString()); var dt2 = new Date(dt.getTime() + 30 * 60000); console.log(dt2.toString()); <script> Excepted result (it works this way for other dates/years): Thu Jan 01 2008 23:30:00 GMT+0300 Fri Jan 02 2008 00:00:00 GMT+0300 But we have: Tue Jan 01 2008 23:30:00 GMT+0300 Wed Jan 02 2008 01:00:00 GMT+0400 1039138 1 ggaren 2014-10-02 23:58:48 -0700 <rdar://problem/18536183>