var date1 = new Date('December 31, 1975, 23:15:30 GMT+11:00');
var date2 = new Date('December 31, 1975, 23:15:30 GMT-11:00');

// December
console.log(date1.getUTCMonth());
// expected output: 11

// January
console.log(date2.getUTCMonth());
// expected output: 0